AQUATIC MIDGES AND SOME RELATED INSECTS 19 



floating by. In the case of larva No. 1 this has only to be done twice, but in Tanytarsus pusio from four 

 to seven times, according to the number of arms present. From time to time the larva pulls down the net 

 between two arms, using the labrum and thoracic feet to collect the particles together into a compact 

 mass, which may then be used for further building operations or may be pressed into the mouth to 

 be consumed. [Mundy, 1909.] 



SILK SPINNING. 



This process has not been treated in any considerable detail by Mundy except 

 that he rightly inferred that the silk was made up of bands of slime or mucus instead of 

 threads. The author has followed the activities of Tanytarsus exiguus in its silk-spinning 

 movements and finds it a very difficult species to observe in this particular. Its chief 

 silk-spinning activities consist of the rapid movements of its head and anterior prolegs 

 in such close proximity to the surface that in spite of the numerous repetitions of the 

 same movement, while applying layer after layer of silk to the rim of its burrow, the 

 author was unable to determine that the head did not play an equally important part 

 in this process. It was more nearly possible to distinguish the use of the prolegs in the 

 work of reinforcing the arms. Here the most characteristic movements were upward, 

 in which movements the head was held somewhat away from the arm as the body 

 encircled it. 



The most satisfactory movements in this process were those concerned in the con- 

 struction of the web mentioned above. The specimen studied in this particular had a 

 tube fastened to the bottom of a glass vessel. This tube had two radiating arms on 

 which the larva spun a single thread. This web was attached to the glass as far out as 

 the larva could reach, then to the nearest arm, and from this arm to the second and 

 down to the glass again on the opposite side. In this process the larva in swinging from 

 one arm to the other repeatedly struck the end with its prolegs while its head projected 

 well beyond. 



The silk is especially viscous, and the particles swept against it by the current readily 

 stick fast. By this means the single thread spun by Tanytarsus exiguus was very eflective 

 in catching particles. At intervals this thread was pulled down and consumed, the 

 labrum and maxillae playing the important part in the process. The prolegs were not 

 seen to be employed in the pulling down or rather pulling in of this single thread, as 

 stated by Mundy. 



ADAPTABILITY. 



The Tanytarsus pusio larvae were taken from flowing water and placed in dishes 

 containing only about a quarter of an inch of water with relatively few fatalities, con- 

 sidering the crude methods employed in removing their burrows. The dead larvae were 

 removed and a small amount of organic debris added. This the larvae raked together 

 in masses near the ends of their burrows and consumed in what seemed tremendous 

 amounts for such small larvae. They simply placed their heads against one side of a 

 mass, and by the motion of the appendages of the head alone the food was passed down 

 their throats in a steady stream. It was apparently fastened together by the silk spun 

 during the process of collecting it together. In this connection Mundy's observation, 



