510 



ILLUSTRATIONS OF DEVELOPMENT. 



Fig- 242, mal, after passing through an inter- 



mediate state, eventually loses its 

 gills and tail, ceases its aquatic, and 

 commences aerial respiration, and 

 shows the aspect, Fig. 242, of the 

 perfect frog. 



Fig. 243 represents the success- 

 ive metamorphoses of the Carcinus 

 mamas, or edible crab, as given by Mr. Couch. A represents the animal 



Fig. 243. 



Development of the crab. 



on its emergence from the egg. It has a hemispherical shield on the 

 head and thorax, with a projecting spine, a tail formed of six segments, 

 the two last being joined laterally. The second form, at B, exhibits a 

 great change: the spine has disappeared, the shield is depressed, the 

 eyes on footstalks ; there are claws, and the tail is often carried bent 

 under the body. When this shell, like its predecessor, has been cast, 

 the third form, C, is assumed, the transition adapting the animal for 

 walking rather than swimming. The final form, D, is taken on at the 

 next moult, and now development ceases, and growth only takes place. 

 Fig. 244 illustrates the metamorphoses of a lepidopterous insect, the 



Bombyx mori, or moth 

 of the silk- worm. From 

 the eggs there arises a 

 caterpillar, which not on- 

 ly possesses the means of 

 locomotion by feet, etc., 

 but also contains within 

 it the rudiments of the 

 organs to be eventually 

 assumed. In this state 



Development of insects. the insect passes under 



the name of a larva, because it is covered with a series of teguments, 



