212 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



clinging to the smooth rock bed of the stream, with from 

 an inch to two inches of water running swiftly over them. 



In Colorado and California the larvas of Bihiocefhala 

 elegantulus^ B. comstocki and JB. doanei and those of 

 Blepharocera jordani have been found more scattered and 

 usually more deeply submerged; this is usually caused, or 

 at least the other condition made impossible, by the broken 

 condition of the stream beds, which are usually composed 

 of separate stones of various sizes rather than of smooth bed 

 rock. The larvae cling firmly to the rock by means of the 

 six ventral suckers (whose structure and mode of action is 

 explained on p. 203), and when disturbed can hold so fast 

 that the body is more readily torn in two than dislodged as 

 a whole. Locomotion, which, though slowly, is freely 

 accomplished, is in a lateral direction; the moving larva 

 loosens the hold of three suckers at a time and swings to 

 one side the fore or hinder half of the body thus released, 

 the suckers again attach this part of the body in its new 

 position, and the other half of the body is loosened and 

 swung over, and thus a slow lateral translation of the larva 

 takes place. 



The larvae appear to feed chiefly on diatoms, although 

 other food is doubtless taken. The older larvae of Blefha- 

 rocera cafitata almost always bear a dorsal, felt-like covering, 

 which is composed of a close growth of diatoms. The 

 most abundant diatom in this growth was one of the stalked 

 Gomphonema. The basis of the covering is the gelatinous 

 mass at the base of the stalked diatoms. Scattered upon 

 and through this mass were individuals of Nitzschia, and 

 several other diatomaceous genera. The covering has a 

 soft, felt-like appearance, is grayish or brownish in color, 

 and does not seem to trouble the larvse. An examination 

 of the alimentary canal of B. cafitata larvae always revealed 

 scores or hundreds of the siliceous tests of the diatoms. 

 •Undoubtedly the larvae live chiefly on the diatoms which 

 live on the rocks in these swift, clear waters. The sluggish 

 habits of the larvae, and their restriction to parts of the 

 stream where the only other possible food is carried swiftly 



