DEVELOPMENT 169 
it has contracted, hardened, and assumed its characteristic form 
and coloration (/). 
Pupal Respiration.— [xcept under special conditions, pup 
breathe by means of ordinary abdominal spiracles. Aquatic 
pupz have special respiratory organs, aoe 
such as the tracheal filaments of Simu- 
hum (Fig. 230), and the respiratory 
tubes of Culex (Fig. 220). 
Pupal Protection. — Inactive and 
helpless, most pupze are concealed in one 
way or another from the observation of 
enemies and are protected from mois- 
ture, sudden changes of temperature, 
mechanical shock and other adverse in- 
fluences. The larve of many moths 
burrow into the ground and make an. 
Cocoon of Chrysopa, 
earthen cell in which to pupate; a large 
after emergence of 
number of coleopterous larvee (Lachno-  imago. Slightly en- 
larged. 
sterna, Osmoderma, Passalus, Lucanus, 
etc.) make a chamber in earth or wood, the walls of the cell 
being strengthened with a cementing fluid or more or less 
silk, forming a rude cocoon. Silken cocoons are spun by 
some Neuroptera (Chrysopide, Fig. 214), by Trichoptera 
(whose cases are essentially cocoons), Lepidoptera, a few Co- 
leoptera (as Curculionide, Donacia), some Diptera (as Cecido- 
myiide), Siphonaptera, and many Hymenoptera (for exam- 
ple, TVenthredinide, Ichneumonidz, wasps, bees and some 
ants ). 
The cocoon-making instinct is most highly developed in 
Lepidoptera and the most elaborate cocoons are those of Satur- 
nde. The cocoon of Samia cecropia is a tough, water-proof 
structure and is double (Fig. 215), there being two air spaces 
around the pupa; thus the pupa is protected against moisture 
and sudden changes of temperature and from most birds as 
well, though the downy woodpecker not infrequently punc- 
tures the cocoon. S. cecropia binds its cocoon firmly to a 
