154 Journal New York Entomological Society. [Vol. xxv. 



ence of yolk in the upper half of the otherwise semi-transparent egg. 

 However, soon after oviposition is terminated the color of the eggs 

 begins to change and to turn into a mottled grey, thence to shining 

 black. This process can be easily watched under a strong lens. It 

 is seen that the black color appears at first in the upper half of the 

 egg on that side which corresponds to the dorsal side of the embryo 

 and in the shape of a symmetrical spot with several branches reach- 

 ing backward about to the middle of the egg (Plate X, fig. 6). In 

 this stage the beginnings of the embryonic development may be seen 

 in the lower part of the egg. In about two to three hours, often 

 sooner for in one instance only one hour was required, the entire 

 egg has turned black. In Chrysops caUidiis, therefore, it is not pos- 

 sible to make any direct observations upon embryonic development. 

 The eggs of another species which I found remain transparent and 

 afford an excellent object for such observations. 



The duration of embryonic development until hatching, is, in C. 

 caUidus, about five days. Eggs laid on July 6, 1916, at 11 A. M., 

 were found hatched on July 11, at 12 o'clock, but had probably 

 hatched in the preceding night or early in the morning. Eggs laid 

 on July 20, at 3:30 P. M., were found hatched on July 25, at 11 P. ^I. 



The time of hatching is almost invariably in the evening soon after 

 sunset or later. Times of hatching recorded were 7:10 P. M., 8 

 P. J\I., on July 6, 1915; 9 P. M. on July 12; 11 :20 P. M. on July 25; 

 8:30 A. M. on July 13; and between 11 P. j\I. and 9 A. M. on August 

 y-8. In one case at least the larvae were observed to hatch in the 

 morning, at 8 130. x\lthough watched, none were seen hatching dur- 

 ing daytime. 



The act of hatching itself is not without interest. In most cases 

 all the larvae hatch at about the same time, each one leaving the egg 

 through its upper pole, and the black surface of the clusters is sud- 

 denly seen covered with a whitish wriggling mass. A number of 

 single larvae may hatch somewhat later and the whole process may 

 take a quarter of an hour. The larvae are very active and decidedly 

 thigmotactic, clinging to each other and forming masses or lumps, 

 which soon loose their hold on the smooth surface of the cluster and 

 drop to the ground or, under normal conditions, into the water. 



It was found that it is absolutely vital for the young larvae to 

 reach water soon after hatching. Larvae which were allowed to drop 



