5° 
Development and Metamorphosis 
to the ancestral fish-like ancestors of all vertebrates. Do then the larvae 
and pupae of insects with complete metamorphosis represent ancestral stages 
in insect evolutionary history? In some degree the larval stage does, but 
in no degree does the pupal. 
Insects are certainly not de¬ 
scended from an animal that, 
like a pupa, could neither move 
nor eat and which had no in¬ 
ternal organs except a nervous 
system, heart, and rudimentary 
reproductive glands. Biologists 
recognize that the exigencies of life during adolescence may profoundly 
modify what might be termed the normal course of development. As 
long as the developing animal is shielded from the struggle for existence, 
is provided with a store of food and protected from enemies by lying in an 
egg-shell or in the body of the mother, it may pursue fairly steadily its reca¬ 
pitulatory course of development; but once emerged and forced to shift for 
Fig. 82.—A bit of degenerate muscle from tussock- 
moth, Hemerocampa leucostigma. Note phago¬ 
cytic cells attacking muscle at the margins. 
(Greatly magnified.) 
Fig. 83.—Degenerating muscle from pupa of giant crane-fly, Holorusia rubiginosa, show¬ 
ing phagocytic cells penetrating and disintegrating the muscle-tissue. (Greatly 
magnified.) 
itself, it must be, at whatever tender age it is turned out, or whatever ancient 
ancestor it is in stage of simulating, adapted to live successfully under the 
present-day and immediate conditions of life. If the butterfly gets hatched 
long before it has reached its definitive butterfly stage, and while it is in 
a stage roughly corresponding to some worm-like ancestors—and from such 
ancestors insects have undoubtedly descended—it must be fitted to live 
