in the scale, retrograding from Campodea, we may even conceive of the stock from which that insect itself has sprung. Campodea within the egg must pass through the stages common to all animals at a like stage of development. There is a stage in the Arthropod type when the young of the insect or crustacean is little else than a footless, imperfectly developed worm. There is even a worm-like larva of an insect allied to the gnats, which corresponds to such a description; and such low insect-larvæ become in turn obviously related in form to certain low creatures allied to the worm kith and kin. One of these low forms (Lindia) is depicted in Fig. 182. This legless organism is related to the well-known "Bear-animalcules," and Rotifers, or Wheel-animalcules. Its jaws resemble those of the larval flies; it has a ringed body, and in other respects exhibits a close likeness to the young of many insects. Possibly, therefore, in some such primitive root, common to a whole host of animals, we may find the dim, ill-defined starting-point whence, led towards Peripatus, and by Campodea, the insect tribes have grown into the brilliance and aërial grace which mark their ranks to-day.

It may not be unprofitable, at the close of our investigation into insect history, to remind ourselves of the great problem which their development has lent its aid in part to solve. At the risk of apparently unnecessary repetition, let us keep in view that every such history, however its individual terms are to be accounted for, forms a link of greater or less importance in demonstrating the great law of evolution, modification, and adaptation as the true method whereby Nature has wrought out the endless variety of the children of life. Especially useful and important, moreover, is the history of the insect as illustrating the changes which the adaptation and modification of the young form may effect in the history of a species. So far from the chrysalis or pupa being a stage in the ancestry of the insects, we have seen that it represents merely a secondary and acquired phase of their development. As Fritz Müller has succinctly formulated it, "the historical record preserved in developmental history is gradually EFFACED as the development strikes into a constantly straighter course from the egg to the perfect animal, and it is frequently SOPHISTICATED by the struggle for existence which the free-living larvæ have to undergo." These words sum up the reason why insects in their metamorphoses exhibit all gradations and shades, from mere moulting of skin to complete change of form through a chrysalis state. Primarily they undergo a metamorphosis because they happen to leave the egg at a relatively early period of development; but they share "metamorphosis"-using the word in the broad sense-with every other living being. It is this plainly discerned series of changes which has chiefly given to the study of entomology its fascination in the past.

One may, however, well be regarded as enunciating a veritable truth when it is stated that the new light which evolution throws on the "why" and "how" a butterfly develops, and a Campodea remains inert, is likely to invest insects, and indeed all other forms of life, with an interest far surpassing that which past years could have imagined or conceived.

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XIII.

THE EVIDENCE FROM THE CONSTITUTION OF COLONIAL OR COMPOUND ANIMALS.

AMONGST the many aspects in which the biologist is accustomed to view the universe of life, few possess a greater interest than that which deals with the nature of animal and plant personality, and with the structural philosophy of the living frame. It is not sufficient for the due investigation of living structures that the forms of animals and plants be compared, and their more obvious differences and peculiarities noted and recorded in scientific annals. Such details and such procedure suffice perfectly for the ordinary run and course of biological work, and form, no doubt, the source of the every-day knowledge on which natural-history science grows and progresses. But a higher era of scientific thought intervenes when philosophy, in its search after relationships and causes, steps forward to correlate and utilise the knowledge observation has acquired. The higher questions of cause and origin are not solved by observation alone. It requires and demands the power of placing facts in appropriate light and shade ere the mutual relations of these facts can be determined, and before their place in the systema naturæ can be definitely ascertained. Judged by this criterion and standard, there are some topics of biology which altogether belong to the region of the abstract and the transcendental. Patient industry may discover, for instance, that a crayfish within the egg repeats, as a stage in its development, the likeness of a form represented to-day by the adult state of some lower crustacean; but it requires philosophy of a transcendental kind to see what that fact means, and what such a discovery implies to the universe of life around. One may perfectly appreciate by ordinary observation that a horse walks on the single toe of each foot, and that its two "splint-bones" represent useless rudiments of other two toes; but it is through an exercise of abstract science alone that we can form the concept of a single-toed horse having arisen from a three-toed one; and from the latter phase of development extend a like thought to that of other living beings. The applications of philosophy to the facts of nature remind one strongly of the most singular and mysterious work of that nature in the production of the living thing itself. In the performance of that function, we require a certain quantity of the substance called "formative

T

material" by the learned in biology, and "protoplasm" by the simple-minded amongst us. This material contains all that is required for the formation of the living frame in so far as the material of that frame is concerned. But in protoplasm alone, we do not find all that is demanded for the growth of the new being. We require, likewise, activity of some kind-potential or real, chemical, physical, or vital, or all three combined; and we depend upon this activity for the combination of the elements of our germ and for the power whereby that germ will in time blossom out into full fruition. So is it, in truth, with the application of knowledge, and with the evolution of the wisdom which arranges our knowledge in its due array. The knowledge we gain is, after all, in itself pure material, on which the potential power of philosophy must exert its influence ere the results of seeking and finding wisdom be fully appreciated. The evolution of a natural fact, or set of facts, to take its place in the array of knowledge we name a science, is therefore matter of higher development than that which merely discovers the facts themselves. Only when philosophy has touched the inert mass of detail, does the harmonious and arranged system spring into view with its power of truly adding to man's knowledge of the universe around and overhead. Only when the search for causation has begun, can our intellectual gains be fully appreciated in our labour of

Untwisting all the chains that tie

The hidden soul of harmony.

Such a topic as presents itself to view in the individuality of animals belongs, it may be with all truth affirmed, to the domain of the philosophy which applies knowledge, rather than to the sphere of mere fact and observation itself. This declaration might sufficiently prejudice the subject in the eyes of readers who might be given to view with suspicion any opinion which apparently lowered fact in the scale of credence. But the philosophy we eulogise, bases its existence on the facts we value. It is the mint-stamp of knowledge, which impresses fact with its popular and received value; inasmuch as, without such impress, the fact itself, however valuable, fails to relate itself to its neighbour truths. Hence, if, in the present chapter, we may venture somewhat within the domain of transcendentalism, it may readily be shown that from the sober basis of facts all our philosophy in reality takes origin. By way of at once illustrating this latter proposition, as well as of laying the foundation-stone of our present study, we may enter upon a recital of the facts of individuality as represented in the living series around us.

A superficial acquaintance with the facts of natural history serves to demonstrate the truth of the axiom that every animal originates, directly or indirectly, from that reproductive body we term

an “ovum” or "egg." As the result of the development of that egg, the animal body becomes the adult; and of the plant the same truth holds good. The seed or germ undergoing development, and passing through stages which are, as a rule, of well-defined nature, at last appears before us as the perfect plant, which, in its turn, will produce blossom and fruit, and will finally lead us back once more to the seed and germ. One marked and very obvious difference between high animals and low animals is found to exist in the different results to which development leads. The lower animal's growth ceases, and its adult condition is attained, at a stage when the development of the higher being has barely begun. It takes but little trouble on nature's part, so to speak, to convert the matter of life of a low animal or plant into a form like itself. On the other hand, the development of a higher animal means time and trouble, to use a familiar expression, and entails the elaboration and building of a complex body from that which is invariably in its first stages uniform and simple in structure.

FIG. 183.-GREGARINA AND ITS
DEVELOPMENT.

Such an animal form as a Gregarina (Fig. 183, d), for instance, presents us with a good example of that simplicity of development and that primitiveness of personality which marks the lower fields of animal life. A gregarina is a minute speck of protoplasm found inhabiting the digestive canal of worms, insects, and crustaceans, as an internal parasite. Each gregarina lives what may be described as the simplest form of existence. Existing in the digestive system of its host, it literally lies bathed amidst the nutriment which that host is elaborating for the repair of its own tissues. Possessing no traces of any of the organs belonging to higher animal existence, the gregarina lives by the absorption of the digested fluids of its host; and save for the slow contractions which are sometimes seen to pass in waves along the surface of its body, no movements can be observed whereby its animality might be popularly confirmed. The course of gregarina-development is by no means complex. The body itself, in lieu of an egg or germ, will, sooner or later, become of globular shape (b). The little solid body, or "nucleus," seen normally (d) in its interior, will vanish by a kind of physiological necromancy, and the body-substance itself will break up and divide into spindle-shaped masses (a), for which the thickened