Development and Metamorphosis 



5 1 



successfully a crawling, squirming, worm-like life. That those insects which 

 hatch as worm-like larvae do in fact owe their wingless, worm-like body con- 

 dition partly to being born in a stage simulating a worm-like ancestor is proba- 



FlG. 84. Degeneration, without phagocytosis, of salivary glands in old larva of giant 

 crane-fly, Holorusia rubiginosa. A, cross-section of salivary gland before degen- 

 eration has begun; B, cross-section of salivary gland after degeneration has set in. 

 (Greatly magnified.) 



bly true. But to be a successful worm demands very different bodily adapta- 

 tions from those of a successful butterfly. And so far does the larval butterfly 

 go, or so far has it been carried, in meeting these demands that nature finds it 

 more economical to get into figurative language 

 or easier to break down almost wholly the larval 

 body after a flew food-supply for further develop- 

 ment has been got and stored away, and to 

 build up from primitive undifferentiated cell begin- 

 nings the final definitive butterfly body, than to 

 make over these very unlike larval parts into the 

 adult ones. The pupal stage, quiescent, non-food 

 taking, and defended by a thick chitinous wall, 

 often enclosed in a silken cocoon, buried in the 

 ground or crevice, or harmonizing so perfectly with 

 its environment as to be indistinguishable from it, 

 is the chief period of this radical and marvelous 

 breaking down and building anew. It is an inter- 

 polated stage in the development of the butterfly 

 corresponding to nothing in the phyletic history; 

 an adaptation to meet the necessities of its life- 

 conditions. To my mind, this is the interpretation of the phenomena of 

 complete metamorphosis. 



FIG. 85. Cross-section 

 of newly developing 

 muscle in pupa of 

 honey-bee, Apis mel- 

 lifica. (Greatly mag- 

 nified.) 



