March, 1913-] LeNG : AqUATIC COLEOPTERA. 33 



or less definite preference for certain environments by which their 

 distribution is governed, while at the same time this distribution is 

 also more or less controlled by such factors as temperature and 

 accident. 



The modifications involve the parts used in locomotion and for 

 attachment to stationary objects, in copulation, in flotation and partic- 

 ularly in respiration. The modifications of the legs of the Dytiscidae 

 to fit them for swimming and of the male front tarsi to assist in hold- 

 ing the female are too well known to need extended mention. The 

 great development of the claws in Parnidse and Elmidje, which, living 

 often in rapid streams, require these elongated and recurved appen- 

 dages to maintain their position, is probably also sufficiently well 

 known. The modification of the claws of Haliplidae larvae to enable 

 them to maintain their position on filamentous algje is not so well 

 known. It is well described by Matheson in the September number 

 of our Journal. In the study of the modifications of vestiture of 

 aquatic insects and their relation to flotation and respiration, such 

 progress has been made by Frank Brocher during the last three 

 years, that a more detailed mention is necessary, particularly as, 

 according to his conclusions, much of the information contained in 

 our books is erroneous. 



The surface of the body of aquatic insects is often observed to be 

 covered at least in part with hair, or in some snout beetles by closely 

 imbricated scales instead, both evidently designed to keep the body dry 

 so that the hairs have received the name of hydrofuge pubescence. 

 Such insects in the water are often observed with a silvery globule of 

 air entangled in the pubescence. Moreover, special appliances for 

 retaining air are found, as in the enlarged coxal plates of the Halip- 

 lidse, and in the arched elytra of the Hydrophilidse, leaving a relatively 

 great space between them and the dorsal aspect of the abdomen, in 

 which the stigmata are situated. The Dytiscidae may be seen com- 

 ing to the surface and hurriedly descending with a globule of air 

 attached to the anal extremity. All these facts seem to point to the 

 conclusion that such insects are thus provided with hairs, etc., to 

 enable them to carry air with them below the surface of the water for 

 breathing purposes. But quite erroneously, if as Brocher has sought 

 to demonstrate such supplies of air are more nearly analogous to that 

 contained in the sound of a fish, and serve the purpose of lessening 



