1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidce 11 



showed their bodies to be covered with many mites. Species of 

 Podophrya and of E pi stylus were also quite frequently observed upon 

 them. Their lack of activity evidently allowed these harmless epizoans 

 to gather on them; after a few daj^s in the aquarium, they were lost. 



The principal egg-laying months are May and August, although 

 the egg-cases of some species may. be found during the entire summer. 

 The eggs, usually placed in "cocoons" (better called egg-cases) of silken 

 structure, hatch out in about seven days. Many eggs are laid by a single 

 individual, thus making up part of the enormous mortality which occurs 

 among the young larva?. 



The silken material which protects the eggs is secreted by the female 

 from glands located in the caudal end of the body. It is applied by the 

 two spinnerets in a manner very much resembling the way a paint brush 

 is used. A continuous flow of silk is laid down at each turn. According 

 to Miger, there are in Hydrous three secretions, each of which has a 

 different use. The first for loose spinning is used for covering the 

 individual egg; the second for constructing the egg-case; and the 

 thud to form the mast at its tip. The function of this mast is a problem, 

 although many suggest that it aerates the case. Several genera place 

 their cases or single eggs below water, so that this supposition does not 

 appear entirely plausible. 



The larvae, when first appearing, are whitish in color, except for 

 the reddish pigment of the ocular areas, but soon the chitinized portions 

 of the body darken. The first duty of the aquatic larvae is evidently to 

 get what is called an "air drink." They lift their heads above water 

 and, with the aid of a pharyngeal pump, draw air into their alimentary 

 canal. Air is also taken into the tracheae through the stigmatic atrium 

 which rests upon the surface film. By thus supplying their bodies with 

 air the larvae become buoyant. Otherwise they would be heavier than 

 water and soon sink, dying because of lack of oxygen. 



The larvae are carnivorous and cannibalistic as well, the different 

 genera varying in their greed. The young larvae feed upon small organ- 

 isms (entomostracans, 1 Tubifex, leeches, etc.) and increase the size of 

 their prey as they themselves increase in size. 



The full-grown larva feeds readily on pollywogs, annelids, fish, and, 

 in fact, almost anything that it can overcome or that is fed to it. It 

 lies in wait for its prey with its jaws extended widely and, as a rule, is 

 half in the water and half out, the caudal end being out. When it begins 



■Il'lophoruss was observed feeding on Simocephalus, Cypris, Cypridopsis, Cyclops, and Canthocampus. 



