METAMORPHOSES OF ANIMALS. 175 



phoses, 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 air-tubes, and breathes in the atmosphere. It passes by, 

 with indifference, objects which before were 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. 



369. 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 

 remains enclosed in its chrysalis state.* During this period 

 of its existence, most extraordinary changes take place. The 

 jaws with which it masticated mulberry leaves are trans- 

 formed 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 elon- 

 gated and narrow. The dorsal vessel is shortened. The 

 ganglions of the thoracic region approach each other, and 

 unite into a single mass. Antennas and palpi are developed on 

 the head, and instead of simple eyes appear compound ones. 



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

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



