26 BULLETIN OF THE BUREAU OP FISHERIES. 



leaves found with egg masses on them were near these trees and were shaded during a 

 part of the day. Mating and egg laying probably takes place in the early evening, as 

 is the habit of the family. 



When infested leaves are brought into the laboratory, the adults begin to emerge 

 in a day or so and continue to transform a few at a time until they have all completed 

 their development. This lack of uniformity in the time of transforming is character- 

 istic of the Chironomidae and is an important factor in their adaptation to the dominant 

 position that they hold in the life of the fresh waters. In the case of Chironomus bra- 

 senice this adaptation makes it a worse pest. 



Dr. Pettit bred his first specimens about the middle of May while at Forest Hill, 

 Mass., and in his note before the Academy of Science he states that a second brood was 

 seen on August i at Pine Lake, Ingham County, Mich. It seems probable that the 

 term "brood" is here rather loosely applied. 



PENETRATING THE EPIDERMIS. 



The author has given evidence above to show that the leaf-mining method of feed- 

 ing seems not to be adopted before mid-larval life, and hence is doubtless a less primi- 

 tive habit than that of the young larvae. 



That this method of feeding is probably impossible for the young larvae seems 

 borne out by observations made upon the behavior of the half-grown larvae in penetrat- 

 ing the epidermis of aquatic leaves. In attempting to induce the larvae to start new 

 burrows the writer removed them from their old ones and placed them on leaves where 

 there were no unoccupied burrows. This work was for the most part rewarded only 

 by observing the larvae searching vainly for their original burrows. If by chance one 

 encountered the burrow of another larva it crept boldly in, only to be met by the owner, 

 who usually administered a sharp nip by means of its mandibles. Since the members 

 of the genus are chiefly herbivorous and therefore for the most part peaceably inclined, 

 the intruder usually retires quickly. It often repeats its attempt to enter the same 

 burrow several times in succession, each time more cautiously, until it finally gives up 

 or in some cases enters an unused part of the burrow and begins feeding. In this case 

 it extends its burrow as a continuation of the original burrow or as a side branch, show- 

 ing that it finds a decided advantage in using a burrow already started. 



In case the larva gives up the attempt to enter an already formed burrow it begins a 

 new one. The first requisite is the spinning of an arch formed of many thicknesses of silk 

 about the size of an ordinary burrow. This, from the author's laboratory observations, 

 is preferably located near another burrow, perhaps because of the water film that always 

 accompanies the burrow. The larva next enters this silken arch, which is about as 

 long as wide, turns itself on its back, and bends its head backward. This position 

 enables the larva to brace its anterior prolegs against the underside of the silken arch 

 and so bring pressure upon its head, which is at such an angle to the surface that the 

 mandibles and the labrum are in contact with the surface of the leaf. In this position, 

 with the head bent backwards a little more than at right angles, it extends its mandibles 

 and rasps its way slowly through the epidermis. The spinning of the arch and the 

 penetrating of the epidermis take over an hour and are doubtless severe tests on the 

 strength of so small a larva. 



