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This laboratory manual encompasses the basic laboratory techniques which start with description about basic laboratory safety rule, cleaning and sterilization methods, bacterial staining techniques, bacterial culturing methods, primary identification and secondary biochemical tests and antibiotic sensitivity tests. It also includes commonly used serological tests, mycological and viral culture and identification technique. High standards of laboratory safety and containment that will ensure healthy working conditions for student, laboratory staff and protection of the environment must be of the greatest priority.
They can only be achieved by careful study of the principles involved followed by practical application to premises, facilities, operating procedures and hygiene. Orientations or short term training must be given to all students and laboratory personnel before they are entirely allowed to use the laboratory. Skull of Spur-winged Goose, phant,. Pectoral arch and fore-limb Skull of Deinotherium,.
Feet of Carnivora,.. Fore-limb of Jer-falcon,. Phoca granlandica,.. Hind-limb of Loon,.. Skull of the Walrus,. Digestive System of the Skull of Jackal,.. Skull of Lion,.. Lung of Goose,. Skull of Beaver,.. Foot of Cormorant and Common Hamster,. Skeleton of Fox-bat,. Head of Vampire-bat and Leg of Curlew, Head of Fox-bat,.. Skull of Hedgehog,. Crested Heron,. European Mole,.. Foot of Ostrich,and Breast- Green Monkey,. Skulls of Orang and EuroxI9. Apteryx Australis,.
Foot of Fowl, and Head of Jaw of Dromatherium,. Skull of Diprotodon, 6II Purple-capped Lory,. Skeleton of Megatherium, 6I2 x Feet and Heads of Inses- Glyptodon clavipes,. Skeleton of Megaceros Hix Foot of Peregrine Falcon, Skeleton of Mastodon, 6I5 and Head of Buzzard,. Skeleton of Mammoth,. NATURAL HISTORY, strictly speaking, and as the term itself implies, should be employed to designate the study of all natural objects indiscriminately, whether these are organic or inorganic, endowed with life, or exhibiting none of those incessant vicissitudes which collectively constitute vitality.
So enormous, however, have been the conquests of science within the'last century, that Natural History, using the term in its old sense, has of necessity been divided into several more or less nearly related branches. In the first place, the study of natural objects admits of an obvious separation into two primary sections, of which the first deals with the phenomena presented by the inorganic world, whilst the second is occupied with the investigation of the nature and relations of all bodies which exhibit life.
The former department concerns the geologist and mineralogist, and secondarily the naturalist proper as well; the latter department, treating as it does of living beings, is properly designated by the term Biology from. Biology, in turn, may be split up into the sciences of Botany and Zoology, the former dealing with plants, the latter with animals; and it is really Zoology alone which is nowadays understood by the term Natural History.
In determining, therefore, the limits and scope of Biology, we are brought at the very threshold of our inquiry to the question, What are the differences between dead and living bodies? In determining this somewhat difficult point, it will be best to examine the differences between organised and unorganised bodies seriatim, and to compare them together systematically under the following heads:a. Chemical Composition.
Organised bodies, on the other hand, are composed of few chemical elements, and these are almost always combined. Furthermore, the combinations are always complex ternary and quaternary compounds , and the elements enter into union in high combining proportions. Finally, the combinations are invariably characterised by the presence of water, and are prone to spontaneous decomposition.
Thus, the great organic compound, albumen, is composed of I44 atoms of carbon, IIo of hydrogen, i8 of nitrogen, 2 atoms of sulphur, and 42 of oxygen. Iron, however, exists in the blood, very probably in its elemental condition; and copper has been detected in the liver of certain Mammalia, and largely in the red colouringmatter of the feathers of certain birds.
Arrangement of Parts. Organised bodies are composed of heterogeneous parts, the relations of which amongst themselves are more or less definite. Organised bodies are always more or less definite in shape, presenting convex and concave surfaces, and being bounded by curved lines. Organised bodies increase by what is often called. To this process alone can the term "growth " be properly applied.
Cyclical Change. Organised bodies are preeminently distinguished by the tendency which they show to pass through spontaneous and cyclical changes. To sum up, all bodies which are composed of an aggregation of diverse but definitely related parts, which have a definite shape, bounded by curved lines and presenting concave and convex surfaces, which increase in size by the intussusception of foreign particles, and which pass through certain cyclical changes, are organised; and it is with the study of bodies such as these that Biology is concerned.
In the foregoing- t has been assumed, for the sake of simplicity, that all living bodies exhibit organisation. It is to be remembered, however, that there are living bodies e. Such bodies are living, but they are not organised. In these cases the distinction from dead matter depends wholly upon the mode of growth, and upon the presence of vital activity as shown by the occurrence of various periodic changes.
The grand and fundamental characters by which living bodies are distinguished from dead bodies are these:-I. Every living body possesses the power of taking into its interior certain foreign materials, and converting these into the substances required to build up fresh tissue or repair waste. By'this power of " assimilation," as it is called, a living body grows.
Living bodies, as they are constantly assimilating fresh matter, are incessantly losing portions of their substance-or, in other words, partial death is a constant accompaniment of life. If our observation be continued for a sufficient length of time, we find that every living body has the power of reproducing its like. That is to say, every-living body has, directly or indirectly, the power of giving origin to minute germs which are developed into the likeness of the parent.
The living body is the seat of energy, and can overcome the primary law of the inertia of matter. It has certain relations with the outer world other than those of mere passivity. However humble it may be, and even if it be permanently rooted to one place, some part or other of every living body possesses the power of spontaneous and independent movement-a power possessed by nothing that is dead. We hlave next to determine-and the question is one of great difficulty-what connection exists between organisation and life.
Is organisation, as we have defined it, essential to the manifestation of life, or can vital phenomena be exhibited by any body Which is devoid of an organised structure? In other words, is life the cause of organisation, or the result of it? And first, what do we mean by life? Life has been variously defined by different writers. Bichat defines it as " tle sum total of the functions which resist death;" Treviranus, as "the constant uniformity of phenomena with diversity of external influences; " Duges, as " the special activity of organised bodies; " and Beclard, as " organisation in action.
In point of fact, no rigid definition of life appears to be at present possible, and it is best to regard it as being simply a tendency exhibited by certain forms of matter, under certain conditions, to pass through a series of changes in a more or less definite and determinate sequence.
As regards the connection between life and organisation, it appears that whilst all organised bodies exhibit this tendency to change, and are therefore alive, all living -beings are not necessarily organised. Many of the lowest forms of life such as the Foraminifera amongst the Protozoa fail to fulfil one of the most essential conditions of organisation, being devoid of definite parts or organs of any kind.
Nevertheless, they are capable of manifesting all the essential phenomena of life; they are produced from bodies like themselves; they eat, digest, and move, and exhibit distinct sensibility to many external impressions. In the face of these facts we are therefore compelled to come to the conclusion that life is truly the cause and not the consequence of organisation; or, in other words, that organisation is not an intrinsic and indispensable condition of vital phenomena.
Such an intrinsic and indispensable condition is, however, to be found in the presence of a uniform " physical basis," to which has been applied the name of " protoplasm " the "bioplasm " of Dr Beale. Without some such a material substratum, or medium upon which to work, no one vital phenomenon can be exhibited. The necessary forces may be there, but in the absence of this necessary vehicle there can be no outward and visible manifestation of their existence.
Life, therefore, as we know it, and as far as zewe know it, may be said to be inseparably connected with protoplasm. In other words, protoplasm bears to life the same relation that a conductor does to the electric current. It is the sole medium through which life can be brought into relation with the external world.
There is, however, as yet, no reason to believe that protoplasmic matter holds any other or higher relation to life, or that vital phenomena are in any way an inherent property of the matter by which alone they are capable of being manifested. As regards its nature, protoplasm, though capable of forming the most complex structures, does not necessarily exhibit anything which can be looked upon as organisation, or differentiation into distinct parts; and its chemical composition is the only constant which can be approximately stated.
It consists, namely, in all its forms, of the four elements, carbon, hydrogen, oxygen, and nitrogen, united into a proximate compound to which Mulder applied the name of " proteine," and which is very nearly identical with albumen or white-ofegg. These extrinsic conditions of vitality are, firstly, a certain temperature varying from near the freezing-point to I or I; secondlay, the presence of water, which enters largely into the composition of all living tissues; thirdly, the presence of oxygen in a free state,-this, like water, appearing to be a sine qua non of life, though certain fungi are stated to offer an exception to this statement.
O The non-fulfilment of any of these conditions for any length of time, as a rule, causes death, or the cessation of vitality; but, as before remarked, life may sometimes remain' in a dormant or "potential " condition for an apparently indefinite length of time. An excellent illustration of this is afforded by the great tenacity of life, even under unfavourable conditions, exhibited by the ova of some animals and the seeds of many plants; but a more striking example is to be found in the Rotifera, or Wheelanimalcules.
These are minute, mostly microscopic creatures, which inhabit almost all our ponds and streams. Diminutive as they are, they are nevertheless, comparatively speaking, of a very high grade of organisation. They possess a mouth, masticatory organs, a stomach, and alimentary canal, a distinct and well-developed nervous system, a differentiated reproductive apparatus, and even organs of vision.
Repeated experiments, however, have shown the remarkable fact, that, with their aquatic habits and complex organisation, the'Rotifers are capable of submitting to an apparently indefinite deprivation of the necessary conditions of their existence, without thereby losing their vitality. They may be dried and reduced to dust, and may be kept in this state for a period of many years; nevertheless, the addition of a little water will at any time restore them to their pristine vigour and activity.
It follows, therefore, that an organism may be deprived of all power of manifesting any of the phenomena which constitute what we call life, without losing its hotd upon the vital forces which belong to it. If, in conclusion, it be asked whether the term " vital force" is any longer permissible in the mouth of a scientific man, the question must, I think, be answered in the affirmative.
Equally unquestionable is the fact that the development of Biological science has progressed contemporaneously with the successive victories gained by the physicists over the vitalists. Still, no physicist has hitherto succeeded in explaining any fundamental vital phenomenon upon purely physical and chemical principles.
The simplest vital phenomenon has in it something over and above the merely chemical and physical forces which we can demonstrate in the laboratory. It is easy, for example, to say that the action of the gastric juice is a chemical one, and doubtless the discovery of this fact was a great step in physiological science. Nevertheless, in spite of the most searching investigations, it is certain that digestion presents phenomena which are as yet inexplicable upon any chemical theory.
This is exemplified in its most striking form, when we look at a simple organism like the Amoeba. This animalcule, which is structurally little more than a mobile lump of jelly,- digests as perfectly-as far as the result to itself is concerned-as does the most highly organised animal with the most complex digestive apparatus. It takes food into its interior, it digests it without the presence of a single organ for the purpose; and still more, it possesses that inexplicable selective power by which it.
In the present state of our knowledge, therefore, we must conclude that even in the process of digestion as exhibited in the Amoeba there is something that is not merely physical or chemical. Similarly, any organism when just dead consists of the same protoplasm as before, in the same forms, and with the same arrangement; but it has most unquestionably lost a something by which all its properties and actions were modified, and some of them were produced. What that something is, we do not know, and perhaps never shall know; and it is possible, though highly improbable, that future discoveries may demonstrate that it is merely a subtle modification of some physical force.
In the meanwhile, as all vital actions exhibit this mysterious something, it would appear unphilosophical to ignore its existence altogether, and the term " vital force. In using this term, however, it must not be forgotten that we are simply employing a convenient expression for an unknown quantity, for that residual portion of every vital action which cannot at present be referred to the operation of any known physical force.
Wve have now arrived at some definite notion of the essential characters of living beings in general, and we have next to consider what are the characteristics of the two great divisions of the organic world. What are the characters which induce us to place any given organism in either the vegetable or the animal kingdom?
What, in fact, are the differences between animals and plants? It is generally admitted that all bodies which exhibit vital phenomena are capable of being referred to one of the two great kingdoms of organic nature. At the same time it is often extremely difficult in individual cases to come to any decision as to the kingdom to which a given organism should be referred, and in many cases the determination is purely arbitrary.
So strongly, in fact, has this difficulty been felt, that some observers have established an intermediate kingdom, a sort of no-man's-land, for the reception of those debatable organisms which cannot be definitely and positively classed either amongst vegetables or amongst animals.
Thus, Dr Ernst Hoeckel has proposed to form an intermediate kingdom, which he calls the Regnum Protisticum, for the reception of all doubtful organisms. Even such a cautious observer as Dr Rolleston, whilst questioning the propriety of this step, is forced to conclude that "there are organisms which at one period of their life exhibit an aggregate of phenomena such as to justify us in speaking of them as animals, whilst at another they appear to be as distinctly vegetable.
The higher plants, on the other hand, possess no nervous system or organs of sense, are incapable of independent locomotion, and are not provided with an internal digestive cavity, their food being wholly fluid or gaseous. These distinctions, however, do not hold good as regards the lower and less highly organised members of the two kingdoms, many animals having no nervous system or internal digestive.
Amongst the Molluscoida, the common sea-mat Flustra is invariably regarded by seaside visitors as a sea-weed. Many of the Protozoa are equally like some of the lower plants Protophyta ; and even at the present day there are not wanting those who look upon the sponges as belonging to the vegetable kingdom. Interinal Structure. In this respect all plants and animals are fundamentally similar, being alike composed of molecular, cellular, and fibrous tissues. Chemical Conmposition.
Still both kingdoms contain identical or representative compounds, though there may be a difference in the proportion of these to one another. Moreover, the most characteristic of all vegetable compounds, viz,, cellulose, has been detected in the outer covering of the sea-squirts, or Ascidian Molluscs; and the so-called "glycogen," which is secreted by the liver of the Mammalia, is closely allied to, if not absolutely identical with, the hydrated starch of plants.
As a general rule, however, it may be stated that the presence in any organism of an external envelope of cellulose raises a strong presumption of its vegetable nature. In the face, however, of the facts above stated, the presence of cellulose cannot be looked upon as absolutely conclusive.
Another highly characteristic vegetable compound is chloriophyll, the green colouringtmatter of plants.. Any organism which exhibits chlorophyll in any quantity, as a proper element of its tissues, is most probably vegetable. As in the case of cellulose, however, the presence of chlorophyll cannot be looked upon as a certain test, since it occurs normally in certain undoubted animals e.
Motor Power. Thus, many animals in their mature condition are permanently fixed, or attached to some foreign object; and the embryos of many plants, together with not a few adult forms, are endowed with locomotive power by means of those vibratile, hair-like processes which are called "cilia," and are so characteristic of many of the lower forms of animal life. Not only is this the case, but large numbers of the lower plants, such as the Diatoms and Desmids, exhibit throughout life an amount and kind of locomotive power which does not admit of being rigidly separated from the movements executed by animals, though the closest researches have hitherto failed to show the mechanism whereby these movements are brought about.
Vatzure of the Food. The unsatisfactory feature, however, in this distinction is this, that even if it could be shown to be, theoretically, invariably true, it would nevertheless be practically impossible to apply it to the greater number of those minute organisms concerning which alone there can be any dispute.
As a broad rule, all plants are endowed with the power of converting inorganic into organic matter. Thefood of plants consists of the inorganic compounds, carbonic acid, ammonia, and water, along with small quantities of certain mineral salts. From these, and from these only, plants are capable of elaborating the proteinaceous matter or protoplasm which constitutes the physical basis of life. Plants, therefore, take as food very simple bodies, and manufacture them into much more complex substances.
In other words, by a process of deoxidation or unburning, rendered possible by the influence of sunlight only, plants convert the inorganic or stable elementsammonia, carbonic acid, water, and certain mineral salts-into the organic or unstable elements of food. The whole problem of nutrition may be narrowed to the question as to the modes and laws by which these stable elements are raised by the vital chemistry of the plant to the height of unstable compounds. To this general statement, however, an exception must seemingly be made in favour of certain fungi, which require organised compounds for their nourishment.
I I all, mediately or immediately, are dependent in this respect upon plants. All animals, as far as is certainly known, require ready-made proteinaceous matter for the maintenance of existence, and this they can only obtain in the first instance from plants.
Animals, in fact, differ from plants in requiring as food complex organic bodies which they ultimately reduce to very much simpler inorganic bodies. The nutrition of animals is a process of oxidation or burning, and consists essentially in the conversion of the energy of the food into vital work; this conversion being effected by the passage of the food into living tissue. Plants, therefore, are the great manufacturers in nature, -animals are the great consumers.
Just, however, as this law does not invariably hold good for plants, certain fungi being in this respect animals, so it is not impossible that a limited exception to the universality ot the law will be found in the case of animals also.. Thus, in some recent investigations into the fauna of the sea at great depths, a singular organism, of an extremely low type, but occupying large areas of the sea-bottom, has been discovered, to which Professor Huxley has given the name of Bathybius.
As vegetable life is extremely scanty, or is altogether wanting, in these abysses of the ocean, it has been conjectured that this organism is possibly endowed with the power-otherwise exclusively found in plants-of elaborating organic compounds out of inorganic materials, and in this way supplying food for the higher animals which surround it. The water of the ocean, however, at these enormous depths, is richly charged with organic matter in solution, and this conjecture is thereby rendered doubtful.
Be this as it may, there remain to be noticed two distinctions, broadly though not universally applicable, which are due to the nature of the food required respectively by animals and plants. In the first place, the food of all plants consists partly of gaseous matter and partly of matter held in solution. They require, therefore, no special aperture for its admission, and no internal cavity for its reception. The food of almost all animals consists of solid particles, and they are therefore usually provided with a mouth and a distinct digestive cavity.
Some animals, however, such as the tape-worm and the Gregarinee, live entirely by the imbibition of organic fluids through the general surface of the body, and many have neither a distinct mouth nor stomach. Secondly, plants decompose carbonic acid, retaining the carbon and setting free the oxygen, certain fungi forming an exception to this law.
The reaction of plants upon the atmo. Animals, on the other hand, absorb oxygen and emit carbonic acid, so that their reaction upon the atmosphere is the reverse of that of plants, and is characterised by the production of carbonic acid. Finally, it is worthy of notice that it is in their lower and not in their higher developments that the two kingdoms of organic nature approach one another. No difficulty is experienced in separating the higher animals from the higher plants, and for these universal laws can be laid down to which there is no exception.
It might, not unnaturally, have been thought that the lowest classes of animals would exhibit most affinity to the highest plants, and that thus a gradual passage between the two kingdoms would be established. This is not the case, however. The lower animals are not allied to the higher plants, but to the lower; and it is in the very lowest members of the vegetable kingdom, or in the embryonic and immature forms of plants little higher in the scale, that we find such a decided animal gift as the power of independent locomotion.
It is also in the less highly organised and less specialised forms of plants that we find the only departures from the great laws of vegetable life, the deviation being in the direction of the laws of animal life. The next point which demands notice relates to the nazture of the differences between one animal and another, and the question is one of the highest importance.
Every animalas every plant-may be regarded from two totally distinct, and, indeed, often apparently opposite, points of view. From the first point of view we have to look simply to the laws, form, and arrangement of the structures of the organism; in short, to its external shape and internal structure. This constitutes the science of morphology iogqr, form, and X6'yo, discourse. From' the second, we have to study the vital actions performed by living beings and the finctions discharged by the different parts of the organism.
This constitutes the science of physiology. A third department of zoology is concerned with the relations of the organism to the external conditions under which it is placed, constituting a division of the science to which the term "distribution " is applied. The term " histology" is further employed to designate that branch of morphology which is specially occupied with the investigation of minute or microscopical tissues.
Physiology treats of all the functions exercised by living bodies, or by the various definite parts or organs, of which most animals are composed. All these functions come under three heads: —I. Functions of Nitrition, divisible into functions of absorption and metamorphosis, comprising those functions which are necessary for the growth and maintenance of the organism. Functions of Repiolvduction, whereby the perpetuation of the species is secured.
Functions of Correlation, comprising all those functions such as sensation and voluntary motion by which the external world is brought into relation with the organism, and the organism in turn reacts upon the external world. Of these three, the functions of nutrition and reproduction are often collectively called the functions of organic or vegetative life, as being common to animals and plants; while the functions of correlation are called the animal functions, as being more especially characteristic of, though not peculiar to, animals.
All the innumerable differences which subsist between different animals may be classed under two heads, corresponding to the two aspects of every living being, morphological and physiological. One animal differs from another either morphologically, in the fundamental points of its structure; or phzysioogically, in the manner in which the vital functions of the organism are discharged. These constitute the only modes in which any one animal can differ from any other; and they may be considered respectively under the qeads of Specialisation of Function and Morphological type.
Specialisation of Function. They differ from one another physiologically in the lmanner in which these functions are performed. In the manner, however, in which the same results are brought about, great differences are observable in different animals. The nutrition of such a simple organism as the Amoeba is, indeed, performed perfectly, as far as the result to the animal itself is concerned —as perfectly as in the case of the highest animal —but it is performed with the simplest possible apparatus.
It may, in fact, be said to be performed without any special apparatus, since any part of the surface of the body may be extemporised into a mouth, and there is no differentiated alimentary cavity. And not only is the nutritive apparatus of the simplest character, but the function itself is equally simple, and is entirely divested of those complexities and separations into secondary functions which characterise the process in the higher animals.
It is the same, too, with the functions of reproduction and correlation; but this point will be more clearly brought out if we examine the method in which one of the three primary functions is performed in two or three examples. Nutrition, as the simplest of the functions, will best answer the purpose. In the simpler Protozoa, such as the Amoeba, the process of nutrition consists essentially in the reception of food, its digestion within the body, the excretion of effete or indigestible matter, and the distribution of the nutritive fluid through the body.
The first three portions of this process are effected without any special organs for the purpose, and for the last there is simply a rudimentary contractile cavity. Respiration, if it can be said to exist at all as a distinct function, is simply effected by the general surface of the body. In a Ccelenterate animal, such as a sea-anemone, the function of nutrition has not advanced much in complexity, but the means for its performance are somewhat more specialised.
Permanent organs of prehension tentacles are present,. In a Mollusc, such as the oyster, nutrition is a much more complicated process. There is a distinct mouth, and an alimentary canal which is shut off from the general cavity of the body, and is provided with a separate aperture for the excretion of effete and indigestible matters. It is not necessary here to follow out this comparison further. In still higher animals the function of nutrition becomes still further broken up into secondary functions, for the due performance of which special organs are provided, the complexity of the organism thus necessarily increasing pari tassu with the complexity of the function.
This gradual subdivision and elaboration is carried out equally with the other two physiological functions-viz. Morphological Type. The second point in which one animal may differ from another is in its "morphological type;" that is to say, in the fundamental plan upon which it is constructed. By one not specially acquainted with the subject it might be readily imagined that each species or kind of animal was constructed upon a plan peculiar to itself and not shared by any other.
This, however, is far from being the case; and it is now universally recognised that all the varied species of animals-however -great the apparent amount of diversity amongst them-may be arranged under no more than half-a-dozen primary morphological types or plans of structure.
Upon one or other of these five or six plans every known animal, whether living or extinct, is constructed. It follows from the limited number of primitive types or patterns, that great numbers of animals must agree with one another in their morphological type. It follows also that all so agreeing can differ from one another. Every animal, therefore, as Professor Huxley has well expressed it, is the resultant of two tendencies, the one morphological, the other physiological.
We have, then, to remember that every member of each of these primary divisions of the animal kingdom agrees with every other member of the same division in being formed upon a certain definite plan or type of structure, and differs from every other simply in the grade of its organisation, or in other words, in the degree to which it exhibits specialisation of function.
All the members of any given sub-kingdom, when examined in their earliest embryonic condition, are found to present the same fundamental characters. As development proceeds, however, they diverge from one another with greater or less rapidity, until the adults ultimately become more or less different, the range of possible modification being apparently almost illimitable. The differences are due to the different degrees of specialisation of function necessary to perfect the adult: and therefore, as Von Baer put it, the progress of development is from the general to the special.
It is upon a misconception of the true import of this law that the theory arose, that every animal in its development passed through a series of stages in which it resembles, in turn, the different inferior members of the animal scale. With regard to man, standing at the top of the whole animal kingdom, this theory has been expressed as follows:-" Human organogenesis is a transitory comparative anatomy, as, in its turn, comparative anatomy is a fixed and permanent state of the organogenesis of man" Serres.
Iin other words, the embryo of a Vertebrate animal was believed to pass through a series of changes corresponding respectively to the permanent types of the lower sub-kingdoms-namely, the- Protozoa, Ccelenterata, Annuloida, Annulosa, and Mollusca-before finally' assuming the true vertebrate characters. Such, however, is not truly the case. The ovum of every animal is from the first impressed with the power of developing in one direction only, and very early exhibits the fundamental characters proper to its sub-kingdom, never presenting the structural peculiarities belonging to any other morphological type.
Thus, many cases are known in which the younger stages of a given animal represent the permanent adult condition of an animal somewhat lower in the scale. To give a single example, the young Gasteropod amongst the Mollusca transiently presents all the essential characters which permanently distinguish the adult Pteropod.
The development of the Gasteropod, however, proceeds beyond this point, and the adult is much more highly specialised than is the adult Pteropod. When organs in different animals agree with one another in fundamental structure, they are said to be "homologous;" when they perform the same functions they are said to be " analogous. They are not analogous, however, since they do not perform the same function, the one being adapted for aerial locomotion, the other being an organ of prehension.
On the other hand, the wings of a bird and the wings of an insect both serve for flight, and they are therefore analogous, since they perform the same function. They are not homologous, however, as they are constructed upon wholly dissimilar plans. There are numerous cases, however, in which organs correspond with one another' both structurally and functionally, in which case they are both homologous and analogous.
A form of homology is often seen in a single animal in which there exists a succession of parts which are fundamentally identical in structure, but are variously modified to fulfil different functions. Thus a Crustacean-such as the lobstermay be looked upon as being composed of a succession of rings, each of which bears a pair of appendages, these appen dages being constructed upon the same type, and being therefore homologous.
They are, however, variously modified in different regions of the body to enable them to fulfil special functions, some being adapted for swimming, others for walking, others for prehension, others for mastication, and so on. This succession of fundamentally similar parts in the same animal constitutes what is- known as serial homology. Thus the composite Hydroid Polypes and the Polyzoa are singularly like one anotherso much so, that they have often been classed together; whereas, in reality, they belong to different sub-kingdoms.
Many other cases of this resemblance of different animals might be adduced, and in many cases these "representative forms" appear to be able to fill each other's places in the general economy of nature. This is so far true, at any rate, that "homomorphous " forms are generally found in different parts of the earth's surface. Thus, the place of the Cacti of South America is taken by the Euphorbiae of Africa; or, to take a zoological illustration, many of the different orders of Mammalia are represented in the single order Marsupialia in Australia, in which country this order has almost alone to discharge the functions elsewhere performed by several orders.
Many homomorphous forms, however, live peacefully side by side, and it is difficult to say whether in this case the resemblance between them is for the advantage or for the disadvantage of either. In other cases we find certain animals putting on the external characters of certain other animals, to which they may be closely related, or from which they may be widely separated in zoological position.
Such cases are said to be examples of "mimicry," and such animals are said to be " mimetic. In all these cases it appears that the mimetic species is protected from some enemy by its outward similarity to the form which it mimics. Finally, there are numerous cases in which animals mimic certain natural objects, and thus greatly diminish their chances of being detected by their natural foes.
Excellent instances of this are afforded by the insects known as Walking-leaves Phyllium and Walking- sticks Phasmide , which respectively present the most singular resemblance to leaves and dried twigs. This term is employed by zoologists to express the empi.
Thus, all animals which possess two condyles on the occipital bone, and possess non-nucleated red blood-corpuscles, suckle their young. Why an animal with only one condyle on its occipital bone should not suckle its young we do not know, and perhaps we shall at some future time find mammary glands associated with a single occipital condyle. Again, the feet are cleft in all animals which ruminate, but not in any other. In other cases the correlation is even more apparently lawless, and is even amusing.
Thus all, or almost all, cats which are entirely white and have blue eyes, are at the same time deaf. With regard to these and similar generalisations we must, however, bear in mind the following three points:I. The various parts of the organisation of any animal are so closely interconnected, and so mutually dependent upon one another, both in their growth and development, that the characters of each must be in some relation to the characters of all the rest, whether this be obviously the case or not.
It is rarely possible to assign any reason for correlations of structure, though they are certainly in no case accidental. The law is a purely empirical one, and expresses nothing more than the result of experience; so that structures which we now only know as occurring in association, may ultimately be found dissociated, and conjoined with other structures of a different character.
Classification is the arrangement of a number of diverse objects into larger or smaller groups, according as they exhibit more or less likeness to one another. The excellence of any given classification will depend upon the nature of the points which are taken as determining the resemblance. Systems of classification, in which the groups are founded upon mere external and superficial points of similarity, though often useful in the earlier stages of science, are always found in the long-run to be inaccurate.
It is needless, in fact, to point out that many living beings, the structure of which is fundamentally different, may nevertheless present such an amount of adaptive external resemblance to one another, that they would be grouped together in any "artificial" classification.
Philosophical classification depends upon a due appreciation of what constitute the true points of difference and likeness amongst animals; and we have already seen that these are morphological type and specialisation of function. Philosophical classification, therefore, is a formal expression of the facts and laws of Morphology and Physiology. It follows that the more fully the programme of a philosophical and strictly natural classification can be carried out, the more completely does it afford a condensed exposition of the fundamental construction of the objects classified.
Thus, if the whale were placed by an artificial grouping amongst the fishes, this would simply express the facts that its habits are aquatic and its body fish-like. When, on the contrary, we obtain a natural classification, and we learn that the whale is placed amongst the Mammalia, we then know at once that the young whale is born in a comparatively helpless condition, and that its mother is provided with special mammary glands for its support; this expressing a fundamental distinction from all fishes, and being associated with other equally essential correlations of structure.
The entire animal kingdom is primarily divided into some half-a-dozen great plans of structure, the divisions thus formed being called " sub-kingdoms. We shall examine these successively, commencing with the consideration of a species, since this is the zoological unit of which the larger divisions are made up.
Naturalists, in fact, are not yet agreed as to whether the term species expresses a real and permanent distinction, or whether it is to be regarded merely as a convenient, but not immutable, abstraction, the employment of which is necessitated by the requirements of classification. The characters in which individuals must resemble one another in order to entitle them to be grouped in a separate species, according to Agassiz, " are only those determining size, proportion, colour, habits, and relations to surrounding circumstances and external objects.
Thus, there are in nature no assemblages of plants or animals, usually grouped together into a single species, the individuals of which exactly resemble one another in every point. Every naturalist is compelled to admit that. The existence of such individual differences is attested by the universal employment of the terms "varieties" and "races. A " race," again, is simply a permanent or " perpetuated" variety.
The question, however, is this-How far may these differences amongst individuals obtain without necessitating their being placed in a separate species? In other words: How great is the amount of individual difference which is to be considered as merely " varietal," and at what exact point do these differences become of " specific" value?
To this question no answer can be given, since it depends entirely upon the weight which different naturalists would attach to any g;ven individual difference. To such an extent do individual differences sometimes exist in particular generatermed " protean " or " polymorphic " genera-that the determination of the different species and varieties becomes an almost hopeless task.
Besides the individual differences which ordinarily occur in all species, other cases occur in which a species consists normally and regularly of two or even three distinct forms, which cannot be said to be mere varieties, since no intermediate forms can be discovered. When two such distinct forms exist, the species is said to be " dimorphic," and when three are present, it is called " trimorphic. In trimorphic plants, the species is composed of three such distinct forms, which'differ in like manner in the conformation of their reproductive organs, though they are otherwise undistinguishable.
Similar cases are known in animals, but in them the differences, though apparently connected with reproduction, are not confined to the reproductive organs. Thus the females of certain butterflies normally appear under two or three entirely different forms, not connected by any intermediate links; and the same thing occurs in some of the Crustacea. What one observer classes as mere varieties, another regards as good and distinct species.
The second point in the definition of species-namely, community of descent-is hardly in a more satisfactory condition, since the descent of any given series of individuals from a single pair, or-from pairs exactly similar to one another, is at best but a probability, and is in no case capable of proof.
In the case of the higher animals it can doubtless be shown that certain assemblages of individuals possess amongst themselves the power of fecundation and of producing fertile progeny, and that this power does not extend to the fecundation of individuals belonging to another different assemblage.
Amongst the higher animals, " crosses " or "hybrids" can only be produced between closely-allied species, and when produced they are sterile, and are not capable of reproducing their like. In these cases, therefore, we may take this as a most satisfactory element in the definition of "species.
That this fertility is often irregular, and may be destroyed in a few generations, admits of explanation, and hardly alters the significance of these undoubted facts. Upon the whole, then, it seems in the meanwhile safest to adopt a definition of species which implies no theory, and does not include the belief that the term necessarily expresses a fixed and permanent quantity.
The production of occasional monstrosities does not, of course, invalidate this definition. Genus is a term applied to groups of species which possess a community of essential details of structure. Families are groups of genera which agree in their general characters.
According to Agassiz, they are divisions founded upon peculiarities of " form as determined by structure. Classes are larger divisions, comprising animals which are formed upon the same fundamental plan of structure, but differ in the method in which the plan is executed Agassiz. Sub-kingd,-oms are the primary divisions of the animal kingdom, which include all those animals which are formed upon the same structural or morphological type, irrespective of the degree to which specialisation of function may be carried.
Impossibility of a Linear Classication. As we have seen, however, the status of any given animal depends upon two conditions-one its morphological type, the other the degree to which specialisation of function is carried. Now, if we take two animals, one of which belongs to a lower morphological type than the other, no degree of specialisation of function, however great, will'place the former above the latter, as far as its type of structure is concerned, though it may make the former a more highly organised animal.
Every Vertebrate animal, for example, belongs to a higher morphological type than every Mollusc; but the higher ALolluscs, such as cuttlefishes, are much more highly organised, as far as their type is concerned, than are the lowest Vertebrata. In a linear classification, therefore, the cuttle-fishes should be placed above the lowest fishes-such as the lancelet-in spite of the fact that the type upon which the latter are constructed is by far the highest of the two.
It is obvious, therefore, that a linear classification is not possible, since the higher members of each sub-kingdom are more highly organised than the lower forms of the next subkingdom in the series, at the same time that they are constructed upon a lower morphological type. Reproduction is the pirocess whereby new individuals are generated and the perpetuation of. Sexual Reproduction. As a rule, the germ-cell is produced by one individual female and the spermatic element by another male ; in which case the sexes are said to be distinct, and the species is said to be "dioecious.
Even amongst hermaphrodite plants, where self-fecundation may, and certainly does, occur, provisions seem to exist by which perpetual self-fertilisation is prevented, and the influence of another individual secured at intervals. Amongst the higher animals sexual reproduction is the only process whereby new individuals can be generated. Non-sexual Replroduction. The processes by which this is effected vary in different. As we shall see, however, the true "individual" is very rarely produced otherwise than sexually, and most forms of agamic reproduction are really modifications of growth.
Gemnmatign and Fission. Fission differs from gemmation solely in the fact that the new structures in the former case are produced by a division of the body of the original organism into separate parts, which may remain in connection, or may undergo detachment. Thus, the Crustacea possess the power of reproducing a lost limb, by means of a bud which is gradually developed till it assumes the form and takes the place of the missing member.
In these cases, however, the process is not in any way generative, and the product of gemmation can in no sense be spoken of as a distinct being or zobid. Another form of gemmation may be exemplified by what takes place in the Foraminifera, one of the classes of the Protozoa. The primitive form of a Foraminifer is simply a little sphere of sarcode, which has the power of secreting from its outer surface a calcareous envelope; and this condition may be permanently retained as in Lagena.
In other cases a process of budding or gemnmation takes place, and the primitive mass of sarcode produces from itself, on one side, a second mass exactly similar to the first, which does not detach itself from its parent, but remains permanently connected with it. This second mass repeats the process of gemmation as before, and this goes on- all the segments remaining attached to one another —until it body is produced, which consists of a number of little spheres of sarcode in organic connection with one another, and surrounded by a shell, often of the most complicated description.
In this case, however, the buds produced by the primitive spherule are not only not detached, but they can only remotely be regarded as independent beings. They are, in all respects, identical with. Another form of gemmation is exhibited in such an organism as the common sea-mat Flustra , which is a composite organism composed of a multitude of similar beings, each of which inhabits a little chamber, or cell; the whole forming a structure not unlike a sea-weed in appearance.
This colony is produced by gemmation from a single primitive being " polypide " , which throws out buds, each of which repeats the process, apparently almost indefinitely. All the buds remain in contact and connected with one another, but each is, nevertheless, a distinct and independent being, capable of performing all the functions of life.
In this case, therefore, each one of the innumerable buds becomes an independent being, similar to, though not detached from, the organism which gave it birth. This is an instance of what is called "' continuous gemmation. This is a simple instance of what is termed " discontinuous gemmation.
The products of the division of the body of the primitive organism may either remain undetached, when they will give rise to a composite structure as in many corals , or they may be thrown off and live an independent existence as in some of the Hydrozoa. We are now in a position to understand what is meant, strictly speaking, by the term "individual. It is most important, however, to comprehend that this is not necessarily or always the case. In such an organism as the sea-mat, the ovum gives rise to a primitive polypide, which repeats itself by a process of continuous gemmation until an entire colony is produced, each member of which is independent of its fellows, and is capable of producing ova.
In such a case, therefore, the term "individual" nmu. The separate beings which compose the colony are technically called " zo6ids. Here the zobids are not permanently united to one another, and the "individual" Hydra consists really of the primitive Hydra, plus all the detached Hydrae to which it gave rise. In this case, therefore, the "individual" is composed of a number of disconnected and wholly independent beings, all of which are the result of the development of a single ovum.
It is to be remembered that both the parent zobid and the " produced zo6ids " are capable of giving rise to fresh Hvdrae by a true generative process. It must also be borne in mind that this production of fresh zobids by a process of gemmation is not so essentially different to the true sexual process of reproduction as might at first sight appear, since the ovum itself may be regarded merely as a highly specialised bud.
The ovarian bud, however, differs from the true gemmae or buds in its inability to develop itself into an independent organism, unless previously brought into contact with another special generative element. The only exceptions to this statement are in the rare cases of true " parthenogenesis," to be subsequently alluded to. Reproduction by Internal Gemnmation. These organisms are nearly allied to the sea-mat, already spoken of, and, like it, can reproduce themselves by continuous gemnmation forming colonies , by a true sexual process, and rarely by fission.
In addition to all these methods they can reproduce themselves by the formation of peculiar internal buds, which are called "statoblasts. When mature they drop off from this cord, and lie loose in the cavity of the body, whence they are liberated on the death of the parent organism.
When thus liberated, the statoblast, after a longer or shorter period, ruptures and gives exit to a young Polyzobn, which has essentially the same structure as the adult. It is, however, simple, and has to undergo a process of continuous gemmation before it can assume the compound form proper to the adult. As regards the nature of these singular bodies, "the invariable absence of germinal vesicle and germinal spot, and their never exhibiting the phenomena of yelk-cleavage, independently of the conclusive fact that true ova and ovary occur elsewhere in the same individual, are quite decisive against their being eggs.
We must then look upon them as gemmtz peculiarly encysted, and destined to remain for a period in a quiescent or pupa-like state. Alternation of Generations. In the former case the produced zobids all resembled each other, and the parent organism which gave rise to them; in the latter case, the produced zo6ids are often utterly unlike each other and unlike the parent, since their functions are entirely different.
The simplest form of the process is seen in certain of the Hydroid Polypes, such as Sertularia. The ovum of Sertularia is a free-swimming ciliated body, which, after a short locomotive existence, attaches itself to some submarine object, develops a mouth and tentacles, and commences to produce zobids like itself by a process of continuous gemmation. These remain permanently attached to one another, with the result that a compound organism is produced, consisting of a number of zobids, or "polypites," organically connected together, but enjoying an independent existence.
None of the zodids, however, are provided with sexual organs; and though there is theoretically no limit to the size which the colony may reach by gemmation, its buds are not detached, and the species would therefore die out, unless some special provision were made for its preservation. Besides these nutritive zobids, however, other buds are produced which differ considerably. These generative zodids derive their nourishment from the materials collected by the nutritive zodids, but only live until the ova are matured in their interior and liberated, when they disappear.
The ova thus produced become free-swimming ciliated bodies, such as the one with which the cycle began. In this case, therefore, the "individual" Sertularia consists of a series of nutritive zo6ids, collectively called the "trophosome," and another series of reproductive zo6ids, collectively called the "gonosome," the entire series often remaining in organic connection. In other forms nearly allied to Sertularia such as Coryne the process advances a step further.
In Coryne the genera-'ive buds, or zobids, do not produce the reproductive elements as long as they remain attached to the parent colony; but they require a preliminary period of independent existence. For this purpose they are specially organised, and when sufficiently matured they are detached from the stationary colony.
It consists of a bellshaped disc, by means of which it is enabled to swim freely; from the centre of this disc depends a nutritive process, with a mouth and digestive cavity, whereby the organism is able to increase considerably in size. The substance of the disc is penetrated by a complex system of canals, and from its margin hangs a series of tentacular processes. After a period of independent locomotive existence, the Medusa attains its full growth, when it develops ova and spermatozoa.
By the contact of these embryos are produced; but these, instead of resembling the jelly-fish by which they were immediately generated, proceed to develop themselves into the fixed Hydroid colony by which the Medusa was originally produced. Still more extraordinary phenomena have been discovered in other Hydrozoa, as in many of the Lucernarida. In these the ovum gives rise as in Sertularia to a locomotive ciliated body, which ultimately fixes itself, becomes trumpetshaped, and develops a mouth and tentacles at its expanded extremity, when it is known as the "hydra-tuba," from its resemblance to the fresh-water polype, or Hydra.
The hydratuba has the power of multiplying itself by gemmation, and it can produce large colonies in this way; but it does not obtain the power of generating the essential elements of reproduction. Under certain circumstances,'however, the hydra-tuba enlarges, and, after a series of preliminary changes, divides by transverse fission into a number of segments, each of which becomes detached and swims away. These liberated segments of the little hydra-tuba it is about half an inch in height now live as entirely independent beings, which were described, by naturalists as distinct animals, and were called Ephyrze.
They are provided with a swimming - bell, or " umbrella," by means of which they propel themselves through the water, and with a mouth and digestive cavity. They now lead an active life, feeding eagerly, and attaining in some instances a perfectly astonishing size the Medusoids of some species are several feet in circumference.
After a while they develop the essential elements of reproduction, and after the fecundation and liberation of their ova they die. The ova, however, are not developed into the free-swimming and comparatively gigantic jelly-fish by which they were immediately produced, but into the minute, fixed, sexless hydra-tuba.
In these are produced generative elements, which give rise by their development to the little fixed creature with which the series began. To the group of phenomena of which the above are examples, the name " alternation of generations " was applied by Steenstrup; but the name is not an appropriate one, since the process is truly an alternation of generation with gemmation or fission.
The only generative act takes place in the reproductive zo6id, and the production of this from the nutritive zo6id is a process of gemmation or fission, and not a process of generation. The "individual," in fact, in all these cases, must be looked upon as a double being composed of two factors, both of which lead more or less completely independent lives, the one being devoted to nutrition, the other to reproduction.
The generative being, however, is in many cases not at first able to mature the sexual elements, and is therefore provided with the means necessary for its growth and nourishment as an independent organism. It must also be remembered that the nutritive half of the " individual " is usually, and the generative half sometimes, compound-that is to say, composed of a number of zo6ids produced by continuous gemmation; so that the zoological individual in these cases becomes an extremely complex being.
These phenomena of so-called " alternation of generations," or "metagenesis," occur in their most striking form amongst the Hydrozoa; but they occur also amongst many of the intestinal worms Entozoa , and amongst some of the Tunicata Molluscoida. By Professor Owen, who first employed the term, parthenogenesis is applied also to the processes of gemmation and fission, as exhibited. Strictly, the term parthenogenesis ought to be confined to the production of new individuals from virgin females by means of ova, which are enabled to develop themselves without the contact of the male element.
The difficulty in this definition is found in framing an exact definition of an ovum, such as will distinguish it from an internal gemma or bud. Moreover, ova are almost invariably produced by a special organ, or ovary. As examples of parthenogenesis we may take what occurs in plant-lice Aphides and in the honey-bee; but it will be seen that in neither of these cases are the phenomena so-unequivocal, or so well ascertained, as to justify a positive assertion that they are truly referable to parthenogenesis in the above restricted sense of the term.
The Aphides, or plant-lice, which are so commonly found parasitic upon plants, are seen towards the close of autumn to consist of male and female individuals. By the sexual union of these true ova are produced, which remain dormant through the winter.
At the approach of spring these ova are hatched; but instead of giving birth to a number of males and females, all the young are of one kind, variously regarded as neuters, virgin females, or hermaphrodites. Whatever their true nature may be, these individuals produce viviparously a brood of young which resemble themselves; and this second generation, in like manner, produces a third,-and so the process may be repeated, for as many as ten or more generations, throughout the summer.
When the autumn comes on, however, the viviparous Aphides produce —in exactly the same manner-a final brood; but this, instead of being composed entirely of similar individuals, is made up of males and females. Sexual union now takes place, and ova are produced and fecundated in the ordinary manner. The bodies from which the young of the viviparous Aphides are produced are variously regarded as internal buds, as " pseudova" i.
Without entering into details, it is obvious that there is only one explanation of these phenomena which will justify us in regarding the case of the viviparous Aphides as one of true parthenogenesis, as above defined. If, namely, the spring broods are true females, and the bodies which they produce in their interior are true ova, then the case is one of genuine parthenogenesis, for there are certainly no males. The case might still be called one of parthenogenesis, even though the bodies from which these broods are produced be regarded as internal buds, or as " pseudova;" for a true ovum is essentially a bud.
If, however, Balbiani be right, and the viviparous Aphides are really hermaphrodite, then, of course, the phenomena are of a much less abnormal character. A hive of bees consists of three classes of individuals-r. A " queen," or fertile female; 2. The "workers," which form the bulk of the community, and are really undeveloped or sterile females; and, 3.
The " drones," or males, which are only produced at certain times of the year.
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