the grasshopper is no longer in a larval or immature condition, but is full grown and adult.

For example of complete metamorphosis among insects we may choose a butterfly, the large red-brown butterfly

FIG. 147.-Metamorphosis of monarch butterfly (Anosia plexippus). a, egg; b, larva; c, pupa; d, imago or adult.

common in the United States and called the monarch or milkweed butterfly (Anosia plexippus). The eggs (Fig. 147, a) of this butterfly are laid on the leaves of various kinds of milkweed (Asclepias). The larval butterfly or butterfly larva or caterpillar (as the first young stage of the butter

flies and moths is usually called), which hatches from the egg in three or four days, is a creature bearing little or no resemblance to the beautiful winged adult. The larva is worm-like, and instead of having three pairs of legs like the butterfly it has eight pairs; it has biting jaws in its mouth with which it nips off bits of the green milkweed leaves, instead of having a long, slender, sucking proboscis for drinking flower nectar as the butterfly has. The body of the crawl

(Fig. 147, 6) is greenish yellow in color, with broad rings or bands of shining black. It has no wings, of course. It eats voraciously, grows rapidly and molts. But after the molting there is no appearance of rudimentary wings; it C is simply a larger wormlike larva. It continues to feed and grow, molting several times, until after the fourth molt it appears no longer as an active, crawling, feeding, worm-like larva, but as a quiescent, non-feeding pupa or chrysalis (Fig. 147, c). The immature butterfly is now greatly contracted, and the outer chitinous wall is very thick and firm. It is bright green in color with golden dots. It is fastened by one end to a leaf of the milkweed, where it hangs immovable for from a few days to two weeks. Finally, the chitin wall of the chrysalis splits, and there issues the full-fledged, great, four-winged, red-brown butterfly (Fig. 147, d). Truly this is a metamorphosis, and a start

FIG. 148.-Metamorphosis of mosquito (Culex). a, larva; b, pupa.

ling one. But we know that development in other animals is a gradual and continuous process, and so it is in the

J

case of the butterfly. The gradual changing is masked by the outer covering of the body in both larva and pupa. It is only

at each molting or throwing off of this unchanging, unyield

ing chitin armor that

we perceive how far this change has gone. The longest time of concealment is that during the pupal or chrysalis stage, and the results of the changing or development when finally revealed by the split

FIG. 149.-Larva of a butterfly just changing into ting of the pupal

pupa (making last larval molt). Photograph
from nature.

case are hence the most striking.

243. Metamorphosis among other animals. Many other animals, besides insects and frogs and toads, undergo metamorphosis. The just-hatched sea-urchin does not resemble a fully developed sea-urchin at all. It is a minute wormlike creature, provided with cilia or vibratile hairs, by means of which it swims freely about. It changes next into a curious boot-jack shaped body called the pluteus stage (Fig. 150). In the pluteus a skeleton of lime is formed, and the final true sea-urchin body begins to appear inside the pluteus, developing and growing by using up the body substance of the pluteus. Star-fishes, which are closely related to sea

urchins, show a similar metamorphosis, except that there is no pluteus stage, the true star-fish-shaped body forming, within and at the expense of the first larval stage, the ciliated free-swimming stage.

A young crab just issued from the egg (Fig. 151) is a very different appearing creature from the adult or fully developed crab. The body of the crab in its first larval stage is composed of a short, globular portion, furnished with conspicuous long spines and a relatively long, jointed tail.

This is called the zoëa stage. The zoëa changes into a stage called the megalops, which has many characteristics of the adult crab condition, but differs especially from it in the possession of a long, segmented tail, and in having the front

half of the body longer than wide. The crab in the megalops stage looks very much like a tiny lobster or shrimp. The tail soon disappears and the body widens, and the final stage is reached.

Interesting examples of metamorphosis occur in nearly all species of the animal kingdom, those mentioned being,

FIG. 151.-Metamorphosis of the crab. a, the zoëa stage; b, the megalops;
c, the adult.

perhaps, the most conspicuous. In many families of fishes the changes which take place in the course of the life cycle are almost as great as in the case of the insect or the toad. In the lady-fish (Albula vulpes) the very young are ribbon-like in form, with small heads and very loose texture of the tissues, the body substance being jelly-like and transparent. As the fish grows older the body becomes more compact, and therefore shorter and slimmer. After shrinking to the texture of an ordinary fish, its growth in size begins normally, although