32 BULLETIN OF THE BUREAU OF FISHERIES. 



which can be swung through an especially wide angle due to their position on the under- 

 side of the labrum. The movements of the lateral arms are so correlated with those of 

 the labrum that the apparent stroking action observed by Taylor might well have been 

 misinterpreted. The correctness of this line of reasoning has been confirmed by the 

 author by direct observation with the low power of the compound microscope on a 

 larva which was feeding with the ventral side up. 



Digestion in Trichocladius nitidellus as in Chironomus brasenice is incomplete, many 

 cells appearing to be unaltered in the course of their passage through the body. 



THE BURROW. 



The burrow, as far as the author has been able to observe, is quite variable. In 

 the older species it is made up of filaments of Spirogyra which have already passed 

 through the body, as Taylor has also observed. In the case of the very young larva 

 the burrow seems to be made up of dark-colored debris due to a different type of food 

 eaten by the young larva. It is found to be made up of organic debris in which diatoms 

 figure very largely. The writer is not sure at what stage the larvae begin to feed upon 

 Spirogyra, but it is certain that specimens not more than one-fourth the size of the 

 mature larva? do feed upon Spirogyra. These larvae have been observed to drag their 

 burrow after them in a manner similar to that described by Lyonet. His observations 

 when translated are approximately as follows : 



Its activity in transporting itself from one region to another is very great and its behavior is 

 peculiar. It extends its head for this purpose, seizes in its teeth all objects which it encounters, retiring 

 quickly without relaxing its hold. The claws of the anterior prolegs hook themselves into the object 

 seized by the teeth, loosening them it elongates itself again in order to seize some more distant object 

 and draw itself forward. 



Taylor does not seem to have noticed this habit, for he states under the heading of 

 "locomotion": 



As the case is not fixed the larva can travel without leaving it. It does not creep like a caddis 

 larva, but jerks itself forward by a few powerful undulations, in which the flexible case participates. 



The older larvae, however, according to repeated observations made on Trichocla- 

 dius nitidellus both in the laboratory and out of doors, show so wide a range of behavior 

 that it is impossible to confirm or disprove any of the above statements. Larvae of 

 this species found living on the algae near the surface in a watering trough were placed 

 in watch glasses and fed diatomaceous debris, which they ate and from which they con- 

 structed tubes in no way different from those characteristic of Chironomus cayugce, as 

 described above. Others, fed on a scant amount of Spirogyra, built no tube at all. 

 About 30 larvae were found at the bottom of a small pool clinging to an old and partly 

 decayed table leg. These had no tubes. It is not difficult to find all intermediate 

 stages between the attached, the free tube, and the larvae without any tubes. 



The food supply seems to be a controlling factor in the nature of the tube built. 

 Since the larva lives on Spirogyra by preference, it eats away all the filaments in its 

 immediate vicinity unless they are very abundant and closely matted. In that case it 

 selects out the filaments which it prefers and simply extends the case. When the food 

 becomes scarce, the larva is able to feed upon whatever debris it finds available, and 

 when feeding in this manner it constructs the tube characteristic of larvae feeding in 

 this manner. 



