52 THE BUTTERFLY. 



composed of many joints movable one upon 

 another, all special distinction between the head 

 and thorax is lost, and their segments are immov- 

 ably soldered into one common tract. This is an 

 exact temporary repetition of the more important 

 distinctive features of the crab and lobster, where 

 the head and thorax are united by a common 

 shield into a cephalo thorax, while the joints of 

 the abdomen are freely movable. This, then, is 

 what Oken meant when he pointedly calls the 

 pupa, Crab. 



When we reach the final stage of the butterfly's 

 life, which we shall now consider, we find its 

 prime distinction to be the clustering of the joints 

 of its body into three perfectly separate regions- 

 head, thorax, and abdomen, each with its peculiar 

 and differently developed appendages. 



Now, since the worm-like or larval stage of in- 

 sects is the most immature, and the crustacean 

 or pupal stage lies intermediate between it and 

 the perfect form, Agassiz urges, in his remark- 

 able " Essay on the classification of insects,"* 

 that worms, Crustacea, and insects are three classes 

 of one type of the animal kingdom, of which 

 worms must be considered the lowest and insects 

 the highest. On the same ground he divides the 

 insects themselves into three groups, and places 



* Smithsonian Contribution to Knowledge, vol. ii. 



