air-breathing animal; its tail and gills disappear, lungs and legs are formed; and finally it lives and moves upon the land.

The nature, the duration, and importance of metamorphoses, and also the epoch at which they take place, are infinitely varied. The most striking changes naturally presenting themselves to the mind, when we speak of metamorphoses, are those occurring in insects. Not merely is there a change of physiognomy and form observable, or an organ more or less formed, but their whole organization is modified. The animal enters into new relations with the external world, while at the same time new instincts are imparted to it. It has lived in water, and respired by gills; it is now furnished with trachæ, and breathes air. It passes by with indifference objects which were before attractive; and its new instincts prompt it to seek conditions which would have been most pernicious during its former period of life. All these changes are brought about without destroying the individuality of the animal. The mosquito, which to-day haunts us with its shrill trumpet, and pierces us for our blood, is the same animal that a few days ago lived obscure and unregarded in stagnant water, under the guise of a little worm. . . .

The different external forms which an insect may assume is well illustrated by the canker-worm. Its eggs are laid upon posts and fences, or upon the branches of the apple, elm, and other trees. They are hatched about the time the tender leaves of these trees begin to unfold. The caterpillar feeds on the leaves, and attains the full growth at the end of about four weeks, being then not quite an inch in length. It then descends. into the ground, and enters the earth to the depth of four or five inches, and having excavated a sort of cell, is soon changed into a chrysalis or nymph. At the usual time in the spring it bursts its skin, and appears in its perfect state in the form of a moth. In this species, however, only the male has wings. The perfect insects soon pair; the female crawls up a tree, and, having deposited her eggs, dies.

Transformations no less remarkable are observed among the Crustacea. The Antifa, like all Crustacea, is reproduced by eggs. From these eggs little animals issue, which have not the slightest resemblance to the parent. They have an elongated form, a pair of tentacles, and four legs, with which they swim freely in the water. Their freedom, however, is of but short duration. The little animal soon attaches itself by means of its

tentacles - having previously become covered with a transparent shell, through which the outlines of the body, and also a very distinct eye, are easily distinguishable. It is plainly seen that the anterior portion of the animal has become considerably enlarged; subsequently the shell becomes completed, and the animal casts its skin, losing with it both its eyes and its tentacles. On the other hand, a thick membrane lining the shell pushes out, and forms a stem, by means of which the animal fixes itself to immersed bodies, after the loss of its tentacles. The stem gradually enlarges, and the animal soon acquires a definite shape. There is, consequently, not only a change of organization in the course of the metamorphoses, but also a change of faculties and mode of life. The animal, at first free. becomes fixed; and its adhesion is effected by totally different organs at different periods of life: first by means of tentacles. which were temporary organs; and afterward by means of a fleshy stem, especially developed for that purpose.

The metamorphoses of the Mollusca, though less striking, are not less worthy of notice. Thus, the oyster is free when young, like the clam, and most other shell-fishes. Others which are at first attached or suspended to the gills of the mother, afterward become free. Some naked gasteropods are born with a shell, which they part with shortly after leaving the egg.

The study of metamorphoses is therefore of the utmost importance for understanding the real affinities of animals, very different in appearance; as is readily shown by the following instances: The butterfly and the earth-worm seem, at the first glance, to have no relation whatever. They differ in their organization no less than in their outward appearance. But on comparing the caterpillar and the worm, these two animals are seen closely to resemble each other. The analogy, however, is only transient; it lasts only during the larva state of the caterpillar, and is effaced as it passes to the chrysalis and butterfly conditions, the latter becoming a more and more perfect animal, whilst the worm remains in its inferior state. .

Similar instances are furnished by animals belonging to all types of the animal kingdom. . . . In the type of the Vertebrata the considerations drawn from metamorphoses acquire still greater importance in regard to classification. The sturgeon and the white-fish are two very different fishes; yet, taking into consideration their external form and bearing merely, it might be questioned which of the two should take the highest rank;

whereas the doubt is very easily resolved by an examination of their anatomical structure. The white-fish has a skeleton, and, moreover, a vertebral column composed of firm bone. The sturgeon, on the contrary, has no bone in the vertebral column. except the spines, or apophyses of the vertebra; the middle part or body of the vertebræ is cartilaginous. If, however, we observe the young white-fish just after it has issued from the egg, the contrast will be less striking. At this period the vertebræ are cartilaginous, like those of the sturgeon, its mouth is also transverse, and its tail undivided. At that period the white-fish and the sturgeon are much more alike. But this similarity is only transient. As the white-fish grows its vertebræ become ossified, and its resemblance to the sturgeon is comparatively slight. As the sturgeon has no such transformation of the vertebræ, and is in some sense arrested in its development, while the whitefish undergoes subsequent transformation, we conclude that, compared with the white-fish, it is really inferior in rank. . .

Nevertheless, the metamorphoses which occur in animals after birth will, in many instances, present but trifling modifications of the relative rank of animals, compared with those which may be derived from the study of changes previous to that period; as there are many animals which undergo no changes of great importance after their escape from the egg, and occupy, nevertheless, a high rank in the zoological series; as, for example, birds and mammals. The question is, whether such animals are developed according to different plans, or whether their peculiarity in that respect is merely apparent. To answer this question, let us go back to the period anterior to birth, and see if some parallel may not be made out between the embryonic changes of these animals, and the metamorphoses which take place subsequently to birth in others.

We have already shown that embryonic development consists in a series of transformations; the young animal enclosed in the egg differing in each period of its development from what it was before. But because these transformations precede birth, and are not therefore generally observed, they are not less important. To be satisfied that these transformations are in every respect similar to those which follow birth, we have only to compare the changes which immediately precede birth with those which immediately follow it, and we shall readily perceive that the latter are simply a continuation of the former, till all are completed,

The young white-fish, as we have seen, is far from having acquired its complete development when born; much remains to be changed before its development is complete. But the fact that it has been born does not prevent its future evolution, which goes on without interruption. Similar inferences may be drawn from the development of the chick. The only difference is that the young chicken is born in a more mature state, the most important transformations having taking place during the embryonic period, while those to be undergone after birth are less considerable, though they complete the process begun in the embryo.

In certain mammals, known under the name of Marsupials (the opossum and kangaroo), the link between the transformations which take place before birth, and those occurring at a later period, is especially remarkable. These animals are brought into the world so weak and undeveloped that they have to undergo a second gestation, in a pouch with which the mother is furnished, and in which the young remain, each one fixed to a teat, until they are entirely developed. Even those animals which are born nearest to the complete states undergo, nevertheless, embryonic transformations. Ruminants acquire the horns and the lion his mane. Most mammals, at their birth, are destitute of teeth, and incapable of using their limbs; and all are dependent on the mother, and the milk secreted by her, until the stomach is capable of digesting other aliment.

If it be thus shown that the transformations which take place in the embryo are of the same nature and of the same importance as those which occur afterward, the circumstance that some precede and others succeed birth cannot mark any radical difference between them. Both are processes of the life of the individual. Now, as life does not commence at birth, but goes still further back, it is quite clear that the modifications which supervene during the former period are essentially the same as the later ones. And hence that metamorphoses, far from being exceptional in the case of insects, are one of the general features of the animal kingdom. We are therefore perfectly entitled to say that all animals, without exception, undergo metamorphoses. . .

It is only by connecting the two kinds of transformation namely, those which take place before and those after birth that we are furnished with the means of ascertaining the relative perfection of an animal. In other words, these transformations

become, under such circumstances, a natural key to the gradation of types. At the same time they force upon us the conviction that there is an immutable law presiding over all these changes, and regulating them in a peculiar manner to each animal. . . . From the facts observed in the study of fossils, we may conclude that the oldest fossil fishes did not pass through all the metamorphoses which our osseous fishes undergo; and consequently that they were inferior to analogous species of the present epoch, which have bony vertebræ. Similar considerations apply to the fossil crustacea and to the fossil echinoderms, when compared with their living types; and it will probably be found true of all classes of the animal kingdom, when they are fully studied as to their geological succession.

VOICES.

(From "Methods of Study in Natural History.")

THERE is a chapter in the Natural History of animals that has hardly been touched upon as yet, and that will be especially interesting with reference to families. The voices of animals have a family character not to be mistaken. All the Canida bark and howl!- the fox, the wolf, the dog, have the same kind of utterance, though on a somewhat different pitch. All the bears growl, from the white bear of the Arctic snows to the small black bear of the Andes. All the cats meow, from our quiet fireside companion to the lions and tigers and panthers of the forests and jungle. This last may seem a strange assertion; but to any one who has listened critically to their sounds and analyzed their voices, the roar of the lion is but a gigantic meow, bearing about the same proportion to that of a cat as its stately and majestic form does to the smaller, softer, more peaceful aspect of the cat. Yet notwithstanding the difference in their size, who can look at the lion, whether in his more sleepy mood, as he lies curled up in a corner of his cage, or in his fiercer moments of hunger or of rage, without being reminded of a cat? And this is not merely the resemblance of one carnivorous animal to another; for no one was ever reminded of a dog or wolf by a lion.