46 BULLETIN OF THE BUREAU OF FISHERIES. 



which they obtain, especially when we learn that these larva? do not burrow but simply 

 wiggle and creep along through the moist and semifluid portions of their environment. 

 That they in all probability live on decaying organic matter, together with the bacteria 

 and mold which are always present in such substances, seems obviously a case of neces- 

 sity. That an aquatic environment offers a greater opportunity for larvae adapted to 

 such a life to select their food is readily seen from the study of even a limited habitat. 



The fact that aquatic larva? kept in confinement will eat animal material is well 

 shown by the observations mentioned above of a larva found eating the tissue of a dead 

 pupa of its own kind. Their presence among filamentous algae suggests that they may 

 also eat out the protoplasmic contents of the larger filaments. It seems probable that 

 various other organisms might become entangled in these filaments and be used as food 

 by these larvae. 



In conclusion, it may be said that the larvae of this group as a whole show a speciali- 

 zation of the mouth parts which fit them to live on soft substances. The various habi- 

 tats in which the larvae are found seem to bear testimony to the organic nature of the 

 food consumed. The uniform failure of all attempts at microscopic analysis of the 

 stomach contents of these larvae suggests the structureless nature of the food taken. 

 It seems apparent, therefore, that, since all decomposing organic matter offers a very 

 similar food supply, the larvae of this subfamily are capable of adapting themselves to 

 a wide range of food substances. The humidity more than any one other factor doubt- 

 less limits this adaptability, since moisture not only aids decay, thus making hard inedi- 

 ble substances available as food, but also serves as a factor of prime importance from 

 the standpoint of respiration to a larva lacking spiracles. 



SUMMARY. 



In the following groups the author has tried to show the more striking differences 

 in the feeding habits of the Chironomidae. In each group the mouth parts and general 

 behavior have been made use of in determining the feeding habits. The stomach con- 

 tents have been depended upon only as a -confirmation of activities actually observed, 

 thus avoiding several errors in connection with the predacious forms. The family as a 

 whole shows a wide range of structural variations and a wider range, if possible, of 

 special adaptations. 



In Group I the larvae, although somewhat variable in habits, can and do live to a 

 very considerable extent upon bacteria, Protozoa, diatoms, small Crustacea and other 

 free-floating aquatic organisms, which they strain from the current driven through their 

 burrows by means of delicate silken nets. 



In Group II the larvae utilize the natural flow of the stream and subsist on the 

 plankton organisms found there. The individuals of this group are usually very numer- 

 ous, but as Group I consists of forms characteristic of quiet water, Group II does not 

 compete with it. 



Group III contains the greater number of the typical Chironomus larvae, known as 

 bloodworms. They are found wherever any considerable accumulation of diatoms 

 and plant debris occurs. In laboratory experiments they were found to be able to sub- 

 sist for considerable periods upon a very scanty supply of food material. Thus, we 

 find them to be a group capable of utilizing and conserving whatever amount of diatoms, 

 algae, and plant debris may chance to fall upon the bottoms of fresh-water ponds. Their 



