ZOOLOGY.

INTRODUCTORY CHAPTER.

"Look on the frame

Of this wide universe, and therein read

The endless kind of creatures, which by name

Thou canst not count."-SPENSER.

ZOOLOGY is derived from two Greek words, and means a knowledge of animals. It teaches their structure, habits, and classification: the person by whom such knowledge has been acquired is a zoologist.

To what kind of creatures the term "animal" is applicable has now to be considered. A party of children, when discussing it in my hearing, settled, in the first instance, that cows, dogs, horses, and all four-footed beasts were animals; then that geese, turkeys, and birds of all kinds were likewise animals. To this there was one dissenting voice-one little fellow stoutly maintaining that the large birds were animals, but that the little birds were not. He was rebuked, however; and the party next proceeded to enrol fishes in their list of animals, which was unanimously agreed to. difference of opinion existed as to whether frogs and snakes should be included; but this was finally done. I ventured to ask if a snail, a spider, and a star-fish might not also be honoured with a place in the list of animals; but the judges, one and all, pronounced the decision of the court, as if by one impulse, and all speaking at the same time-"No, no; such creatures are not animals at all."

A

The naturalist does not, however, use the term "animal" in so restricted a sense; he includes in it all organized existences which do not belong to the vegetable tribes; and, beginning with those which are so minute as to be unseen, save by the assistance of the microscope, rises through the various tribes of animals, until he attains to man himself.

It is worthy of remark, however, that the beings which the children agreed to place together do, in reality, constitute the group to which the highest rank is assigned. They are distinguished by one very obvious characteristic they have a skull and back-bone. The back-bone, as every one knows, is composed of joints, or vertebræ ; hence all animals possessing these are called vertebrate; and, of course, those in which the skull and back-bone are wanting are called invertebrate.

According to Agassiz,* the number of vertebrate animals may be estimated at 20,000; and the entire number of species of all the animals now living at 250,000. At first sight it seems a hopeless task for man to attain to any

* Agassiz and Gould, "Principles of Zoology."

knowledge of such a multitude, and this feeling is increased if we turn our attention to species now extinct, but whose remains are known to us in a fossil state. Supposing that the entire number of fossil species only equalled those which are now living, we have altogether, at what Agassiz considers a very moderate computation, half a million of species.

But though one man could of himself do little, the combined exertions of many labourers, working at the same time in various countries, may do much. And as each generation transmits, by means of books, the knowledge it has acquired, each successive generation starts on its researches from the vantage ground gained by the labours of its predecessors.

It is obvious, however, that in order that men may be enabled to preserve and disseminate their knowledge, the entire animal kingdom must be divided into provinces, well defined and properly named; and as each province in a country is subdivided into counties, baronies, parishes, and townlands, so each in the animal kingdom is parcelled out into smaller divisions according to established rules, and known by distinctive appellations.

How is this to be accomplished? If we turn to the vertebrate animals, we might say that beasts walk on the ground, birds fly in the air, fishes swim in the sea; and this would be quite true, and in a popular and general sense quite correct. But it is not sufficiently precise and definite for the zoologist. He asks, Is the bat to be classed as a bird, because it flies in the air? Is the whale to be regarded as a fish, because it swims in the sea ?

Questions such as these may be discussed with great advantage, and with manifest pleasure, by a class of learners who are under the management of a judicious and well-informed teacher. By queries addressed to each in succession, he engages them all in the inquiry; elicits whatever information they possess; makes each feel as if he himself was engaged in solving a problem of considerable interest; and when he has led them to the very boundaries of their knowledge, should they be still unable to expound the point in question, they are alive to its importance, and prepared to receive such information as he may think fit to impart. His words then fall like seed upon good soil, and bear fruit abundantly.

I well remember the lively interest excited in a class of intelligent girls by the discussion of the question, if a bat, because it could fly in the air, should be considered a bird? The answers went to show that there were important points of difference between them. The bird was covered with feathers-the bat with fur; the bird had a horny beak-the bat, a mouth with teeth of a peculiar form; and finally, the young bird was hatched from an egg-the young bat, on the contrary, was born alive, and suckled by the parent.

On one occasion the question, if the whale was a fish, was discussed at greater length by counsel learned in the law, and before a judge and jury. In New York, many years ago, a dealer in oil refused permission to a government inspector of fish oil to examine his stock, alleging that he had no oil in his store but whale oil; and as the whale was not a fish, the officer had no business with it, nor was it liable to any duty as fish oil. The government, however, did not admit the plea, and the point came before a legal tribunal for decision. On behalf of the government it was argued that the whale was always spoken of as a fish by those engaged in the fishery, a fact which was implied in the very term, "whale fishery;" that in Natural History books of high anthority, of which a great pile was produced in

evidence, the whale was classed among fishes; and that whale oil had always been regarded as fish oil, and had been uniformly charged with duty as such. Counsel on the other side contended that the language of uneducated seamen should not be regarded as evidence, and that the classification in old books of Natural History, to which reference had been made, was founded on a very imperfect knowledge of the structure of the animals so arranged; but that if ancient records were to be referred to, he would go to one more ancient than any other he would go to the Mosaic record of the creation itself, and would show that whales even there were mentioned distinct from fishes; for we read that "God created great whales, and every living creature that moveth, which the waters brought forth abundantly after their kind." The points of difference between whales and fishes were, he insisted, numerous, striking, and sufficient to render it needful to place creatures so essentially dissimilar in different classes.. The fish breathes by gills, the whale by lungs; the blood of the fish is cold; that of the whale is warm; the heart of the fish has two compartments, that of the whale has four; the young of the fish is produced from spawn, that of the whale is born alive, and is suckled and tended by the mother with the most affectionate solicitude. Notwithstanding these arguments-which, so far as the Natural History question is concerned, are quite conclusive-the jury, after the trial had continued for three days, returned a verdict to the effect that the whale oil should be regarded as fish oil. There can be no doubt that such was the intention of the Act; the legislature, the very next session of Congress, amended the wording of it, in order that all ambiguity might for the future be avoided.

It is obvious, from these two examples, that the structure of the animal frame must form the only sure basis for our classification. That structure is adapted with the most consummate wisdom to the medium, whether air or water, which the animal is to inhabit, and to the conditions under which it is to live; and just in proportion as our knowledge is accurate with regard to each particular species, and comprehensive as regards its affinities to others, so will our classification be good or otherwise.

The principle just laid down is applicable to the whole animal creation. This has been spoken of as consisting of vertebrate and of invertebrate animals. To the genius of Cuvier, however, we are indebted for our first knowledge of the fact, that there exist differences among the invertebrate animals so great as to justify their division into three great groups, according to peculiarities in their nervous system. We are thus enabled to divide the entire animal kingdom into four great groups, or sub-kingdoms:

I. VERTEBRATED animals, or Vertebrata.

INVERTEBRATE.

II. Soft-bodied animals, or Mollusca. III. Articulated animals, or Articulata. IV. Radiated animals, or Radiata.

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We shall begin with the examination of those whose organization is the most simple, and gradually ascend to those in which it is the most complex. The radiated animals, therefore, have the first claim on our attention, and

in the next chapter you will find I shall introduce you to some members of this very ancient, though unseen fraternity. You may not, perhaps, have far to go for the introduction. More viewless than the ghost of Hamlet's father, you see them not, yet they are in multitudes around you. Some may even have done you the favour of selecting your bodily frame as their habitation, and, free alike from rent and taxes, laugh to scorn all attempts. to serve them with "notice to quit."

CHAPTER II.

RADIATED ANIMALS.

"Think not that anything HE hath vouchsafed to create is unworthy thy cognizance, to be slighted by thee. It is pride and arrogance, or ignorance and folly, in thee so to think."-RAY.

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Fig. 1.

I HAVE placed at the beginning of this chapter the figure of a common star-fish, or "five-fingers." The limbs or arms are arranged like rays proceeding from a centre, and from this circumstance it is termed a rayed," or "radiated animal." All with this rayed appearance have, of course, the same appellation, and, along with others, constitute the class RADIATA.

The rayed appearance is not, however, so obvious in many of these animals as in the star-fish. In the Sea Urchin we find it in the arrangement of certain parts of the covering, though not in the outline of the body. We can trace it in the bodies of the common elly-fishes, and in the parts surrounding the mouths of some of the Polypes. But there we are obliged to stop; we can follow it no further. In like manner the nervous system, so far as it has been traced, presents a radiated arrangement. But here also the clue which has guided our path for a certain distance eludes our grasp, and we meet animals in which no nervous system has as yet been discovered. The consequence is, that certain tribes have been placed in this division, simply because zoologists, in the present state of their knowledge, knew not where else they could be placed.

With more careful and extended research, some of the evils of this course have become apparent. It has been found that germs of aquatic plants, which in their young state have the power of moving about, have been classed as animalcules. Other vegetable productions the botanist has claimed as belonging to his dominion, and transferred them accordingly from the nimal kingdom; and zoologists of reputation assert that there are now

among the radiate animals some that ought to have a higher rank, and should, if justice were done to their merits, be promoted to the class Articulata, and some even to the Mollusca. In fact, the assemblage is, in many respects, a motley one; insomuch that a respectable star-fish of an established position in society, and wishing to keep his distance from equivocal companions, might be inclined to say, like Sir John Falstaff, "I'll not march through Coventry with them, that's flat."

I must, however, keep to our present classification until a more perfect be established, taking care to indicate the points where the progress of science, during the last few years, has suggested the idea of change. In this way, the reader may consider that "coming events cast their shadows before, and that the best arrangement that can now be given should be regarded as provisional, not permanent. With this explanation we will now enter on They are divided into four

the consideration of the Radiated animals. classes, viz. :

Infusoria, or Infusory Animalcules.

Entozoa, or Internal Parasites.

In casting our eyes over the earth and seas, the animal world that we actually behold constitutes only a part of the animal creation. Besides those that are hid in the sanctuary of the forest and the depths of the ocean, there are tribes which inhabit great caverns and subterranean waters, and that are specially adapted for dwelling in a world where darkness ruleth, and

Light "never comes, that comes to all."

And there are others-and to these our attention is now to be directed—that escape our notice, either by their own minuteness or by their dwelling-place. To this unseen world of animal existence this chapter is to be devoted; it comprises two classes of Radiate Animals-the Infusory Animalcules, which the microscope brings before our eyes, and the Internal Parasites, that live hidden from observation within the bodies of other animals.

I may mention, for the sake of some of my readers, that the word "animalcule" means a "little animal;" and that the term "infusory has reference to their being easily procured by making an infusion of animal or vegetable matter, and allowing it to stand exposed to light and heat, such as the window of a sitting-room would afford. If a drop of the thick scum that may after a few days have gathered on the surface be placed between two plates of glass under the microscope, a busy world of animated existence will be revealed to view; and in that little film of water may be seen

* Sponges are not included, as naturalists are not yet agreed as to their real nature.