354 METAMOEPIIOSES OK? ANIMALS. 



nicious 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. 



551. Every one is familiar with the metamorphoses of the 

 silk-worm. On escaping from the egg the little worm or 

 caterpillar grows with great rapidity for twenty days, when it 

 ceases to feed, spins its silken cocoon, casts its skin, and re- 

 mains inclosed in its chrysalis state.* During this period of 

 its existence most extraordinary changes take place. The jaws 

 with which it masticated mulberry leaves are transformed into 

 a coiled tongue, the spinning organs are reduced, the gullet 

 is lengthened and more slender, the stomach, which was nearly 

 as long as the body, is now contracted into a short bag, the 

 intestine, on the contrary, becomes elongated and narrow ; 

 the dorsal vessel is shortened. The thoracic nervous ganglia 

 approach each other, and unite into a single mass. Antennae 

 and palpi are developed on the head, and simple eyes are 

 exchanged for compound ones. The muscles, which before 

 were uniformly distributed, are now gathered into masses. 

 The limbs are elongated, and wings spring forth from the 

 thorax. More active motions then reappear in the digestive 

 organs, and the animal, bursting the envelop of its chrysalis, 

 issues in the form of a winged moth. 



552. The different external forms which an insect may 



assume is well illustrated by one 



i f 



Fig. 369. which is unfortunately too well known 



in this country, namely, the canker- 

 worm (fig. 369). Its eggs are laid on 

 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 its full growth at the end of about four 

 weeks, being then not quite an inch in length. It then 

 descends to the ground, and enters the earth to the depth of 



* In the raising of silk-worms this period is not waited for, but the 

 animal is killed as soon as it has spun its cocoon. 



