91 



They may be recognized by their uniformly cylindrical bodies, 

 small heads, enclosed in an opaque crust, and with a bi- 

 lobed foot-like process bearing a dense brush of curved bristly 

 hairs extending forward beneath it. At the posterior end of the 

 body is a pair of false feet, also characteristic, each bearing a 

 circlet of retractile hooks. The head is smaller relatively than 

 that of the larva of Corethra, but under the microscope the parts 

 appear almost as complicated. The structures present, however, 

 are mainly in the nature of biting organs, the parts having 

 to do with perception being here poorly developed. Thus the 

 jaws are well developed, the edges of the mouth-opening 

 are furnished with numerous teeth and hooks, and the labium is 

 a broad plate with strongly toothed edge, while, on the other hand 

 the eyes and autennie are very small. All this corresponds wjth 

 what is known of the food of the larvse. Their digestive tube is 

 often jtilled with a brown granular material, consisting, as nearly 

 as can be made out with the microscope, of decomposed organic 

 matter, containing great numbers of bacteria and a good many 

 empty frustules of daitoms. In one example was found the frag- 

 ments of an insect. The organs for mastication, complicated as 

 they are, would hardly be equal to the com.plete obliteration of 

 the cell-structure of plants and animals, were these the aliment 

 upon which the larvte depended; and I believe that the material 

 in the alimentary canals examined was dead when taken. The 

 diatoms were not more freequent than they would be if taken 

 in the slimy coating which collects on submerged objects. The insect 

 fragments, which were of rather large size, bore evidence of having 

 formed a rejected skin; while the abundance of bacteria among 

 the alimentary contents points also in the same direction. 



The larvae are often of a blood-red color. They swim by a 

 wriggling movement when in open water, but commonly live at 

 the bottom, under stones and rubbish, where they construct gal- 

 leries of agglutinated sand in which numbers live together. They 

 may be found in water at all seasons of the year, even under the 

 ice in winter. Quite a number of species are represented by the 

 larvaj taken at Quincy, and some of the forms described below 

 may represent several related species instead of one. 



The pupae differ from those of Corethra in having cottony tufts 

 or antler-shaped fleshy respiratory appendages on each side of the 

 thorax; but some apparently lack these structures. Those with the 

 cottony tufts were common in the galleries under rocks. The ones 

 with antler-shaped respiratory structures were taken at the surface 

 in the bay, and may prove to be free-swimming. Several of these 

 latter had the posterior part of the body enclosed in the larval 

 skin. 



The winged adults were emerging at the surface of the bay 

 August 8. Those captured, nearly all females, were brought in by 

 the stirf ace-net, and are probably among the smallest of the genus, 

 being only about .08 inch long. Color, pale yellow, with three 



