300 INEZ WHIPPLE WILDER. 



The food of larvae during the aquatic period consists mainly 

 of little copepods and occasionaly very small aquatic insect 

 larvae. Mingled with the debris of such food in the stomach and 

 intestine, there are usually found considerable quantities of sand 

 and disintegrating vegetable matter, the ingestion of which is 

 incident to the capture of the living food. The mouth opening 

 does not extend very far back and it is equipped at each angle 

 with a labial fold (//, Fig. 17) so arranged that when the lower 

 jaw is depressed the folds are stretched across the angles making 

 the orifice almost circular in form and directed slightly downward. 

 This is evidently an adaptation to the capture of such food forms 

 as may be scooped up or sucked in from among the sediment 

 at the bottom or upon the surfaces of decaying leaves. 



The respiration during the larval period is accomplished by 

 means of the three pairs of external gill bushes. Although these 

 consist of relatively few filaments, they are held so widely 

 outspread in the water as to render their position the most ad- 

 vantageous one possible to the performance of their function. 

 When the larva is disturbed, however, as by opposing pressure 

 applied to the lateral surfaces of the head, the gills are quickly 

 drawn back and held closely appressed against the sides of the 

 body, a protective reflex the efficiency of which is shown by the 

 fact that one never finds larvae with the gills injured. 



With four gill slits upon each side, it would seem that the 

 mechanism must be present for producing a flow of water through 

 the mouth and pharynx and out over the gills, yet I have never 

 been able to detect the slightest evidence of such a current, or 

 of the rhythmic movements of the floor of the mouth and pharynx 

 such as would be necessary to produce it. Occasionally there 

 may be observed, however, a single, vigorous little movement of 

 the gill bushes, which is undoubtedly for the purpose of assisting 

 diffusion by hastening the change of the water in contact with the 

 gills. This movement is usually performed once or twice when 

 the larva comes to rest after vigorous swimming. The usual 

 position of the larvae when at rest, upon or among decaying leaves 

 just below the surface of the water, gives natural access to the 

 region of the water which is most completely aerated. 



The gill filaments present a certain glistening white appearance 



