DEVELOPMENT 



169 



FIG. 214. 



imago, 



sughtiy en- 



it has contracted, hardened, and assumed its characteristic form 

 and coloration (F). 



Pupal Respiration. Except under special conditions, pupae 

 .breathe by means of ordinary abdominal spiracles. Aquatic 

 pupae have special respiratory organs, 

 such as the tracheal filaments of Simu- 

 lium (Fig. 230), and the respiratory 

 tubes of Culex (Fig. 229). 



Pupal Protection. Inactive and 

 helpless, most pupae 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 larvae of many moths 

 burrow into the ground and make an 

 earthen cell in which to pupate; a large 

 number of coleopterous larvae (Lachno- 

 sterna, Osmo derma, Pa-ssalus, 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 (Chrysopidae, Fig. 214), by Trichoptera 

 (whose cases are essentially cocoons), Lepidoptera, a few Co- 

 leoptera (as Curculionidae, Donacia), some Diptera (as Cecido- 

 myiidae), Siphonaptera, and many Hymenoptera (for exam- 

 ple, Tenthredinidae, Ichneumonidae, wasps, bees and some 

 ants). 



The cocoon-making instinct is most highly developed in 

 Lepidoptera and the most elaborate cocoons are those of Satur- 

 niidae. 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. v$\ cecropia binds its cocoon firmly to a 



