June-Sept., 1919.] MURPHY '. EGG-LAYING OF BRACHYCENTRUS. 155 



entirely or partially submerged, with no air evident clinging to the 

 body, she will excitedly walk around over the stones from three to 

 five minutes. Suddenly she rises and extrudes the egg mass, attach- 

 ing one end to some support. This accomplished, she slowly and very 

 weakly crawls from the water. 



The egg mass, Fig. 10, consists of fifty to one hundred eggs 

 embedded in a gelatinous matrix. The mass is dark-green at first, 

 irregular in shape, three millimeters long by one and one-half wide. 

 It soon swells to about three times its original proportions. A coat- 

 ing of sediment makes concealment almost perfect even while the 

 mass waves to and fro in the current. The egg is dark-green and 

 spherical. 



Embryonic development is completed in from twenty-one to 

 twenty-eight days. At the time of hatching, the abdomen starts to 

 straighten, the legs are thrust downward and the chorion is ruptured 

 in the region of the second thoracic segment, diagonally opposite the 

 point of pressure of the legs and abdomen. With the raising of the 

 head, the chorion is split still farther. Biting with the mandibles 

 and pushing with the legs, the larva crawls out, leaving the exuvia 

 inside the chorion. Examination of this cast skin shows a small 

 chitinous tooth in the region of the clypeus. This so-called " hatch- 

 ing tooth," which, according to Siltala, is common to all Trichoptera, 

 apparenly is not functional in this species. 



The larvse leave the egg mass at once, hastily scramble over 

 stones and sticks into the quieter eddies close to the bank. There 

 they feverishly set about case building. Chewing off a piece of 

 plant material here, gathering a bit of bark or root fiber there, 

 covering all with a generous supply of silk, they fashion splendid 

 little cases. After the first row, which is more or less circular at 

 first and is altered later, they are square in cross section. The larva 

 holds the case with the mesothoracic legs, puts the silk-coated ma- 

 terial in place with prothoracic legs, and tightly shoves it down with 

 the metathoracic legs. Then the larva turns to the next side and 

 puts on a piece of material there and so proceeds to each side in 

 turn. 



The cases are completed in about five hours. The larvae then 

 start to eat. For the first two weeks the food consists entirely of 

 diatoms such as Meridion, Cymbclla, Navicula, Cocconcma, Fragil- 



