Development and Metamorphosis 51 
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- 
Fig. 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 new 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.) 
