3O4 E. H. STRICKLAND. 



stretch from one rake to the next, thus forming a very fine 

 strainer which allows water to pass through it, but retains any 

 small organisms, such as the diatoms, on which the larva subsists. 

 By means of a curious flicking motion the^e fan- can be closed 

 and their contents brushed into the mouth orifice. Here are 

 situated two large glands (Plate IV., Figs. 9 and 10 (d)) on the 

 dorsal side- of the pharynx, whose function appears never to have 

 been determined. They are covered with an apparently porous 

 membrane which is clothed with short stout hairs. It would 

 seem that they secrete some sticky material onto these hairs 

 which removes the particles of food from the rakes when the 

 latter are brought in contact with them. 



It is usually stated that the fans are used to set up currents 

 in the water and thus sweep food toward the mouth. My 

 observations, however, lead me to believe that they act as a 

 "strainer" and this is supported by the fact that, living as these 

 larvae do, in the swiftest currents, such movements would be 

 useless. 



The salivary glands are very large and secrete powerful silken 

 threads which are used by the larvae as anchor lines to hold them 

 in an upright position no matter how strongly the current of 

 water. may flow. 



Although the larvae appear to be very sluggish, they can move 

 about actively on the rocks by a lopping motion similar to that 

 of the geometrid larva. It is interesting to note the care with 

 which these larvae, when thus moving about, assure themselves 

 that the adhesive disc of the prothoracic leg is firmly attached 

 before relaxing the anal disc and vice versa. Respiration is 

 accomplished by means of retractile finger-like blood gills, 

 normally three in number, which are situated on the dorsal 

 surface of the last abdominal segment just above the anus. 

 These gills, which can be distended at will by the insect, by means 

 of blood pressure, are apparently inadequate for use in any but 

 rapidly flowing water which contains plenty of oxygen, for if the 

 larva? be placed in a jar of still water very few will survive for 

 more than eight hours, though life may be prolonged for two or 

 three days by placing them in small numbers in I'etri dishes 

 containing only sufficient water to just cover them. 



