602 Cut PING 
curved at the middle. The anterior end has amicropyle (Plate LVII, 44). 
The chorion is grayish white, but sometimes slightly pink. The surface 
is reticulated with hexagonal markings. 
Hatching 
The egg can hatch in salt water, in lake water, or in tap water. Tem- 
perature has marked influence on the development of the egg, for under 
a temperature of between 18° and 20° C., hatching did not take place 
until the end of the third day, while under a temperature of 33°, eggs 
began to hatch after seventeen hours but most of them were killed soon 
afterward. 
As the embryo develops, the mouth and the claws of the prolegs are 
more or less visible through the chorion. The body is bent in the egg 
shell. The movement of the claws gives an appearence of wave motions. 
The mouth parts frequently gnaw on the inside of the chorion, producing 
a wedge-shaped transparent part. The head breaks the chorion and 
the opening is enlarged by the forcing-out of the thorax. While the body 
is wriggling outside, the claws of the last pair of prolegs often hold onto 
the broken edge of the shell. The larva must struggle before being freed. 
The emergence usually takes from thirty to forty seconds. 
PROTECTION 
Ephydra subopaca has several interesting characteristics that serve 
for protection throughout all the stages in the life cycle. First, it has 
protective coloration. The egg is grayish opaque and can scarcely be 
seen when at the bottom of the water; it is sometimes slightly pinkish and 
is thus more easily confused with decayed plant materials in the salt pools. 
While crawling in shallow pools, the larva gathers dirt all over its body, 
making it resemble the color of the muddy bottom and also that of the 
floating scums. When the larva is mature and ready to pupate, its 
hypodermis becomes hardened and gradually turns brown, resembling 
the color of the plant matter on which the pupa perches. The coloration 
of the adult, as has been described, harmonizes also with its background. 
Boards, logs, scums, or the surface of soft mud in the temporarily dried 
areas, with a number of flies scattered here and there, look concolorous— 
that is, uniformly dull brown; thus a swarm of flies can hardly be 
distinguished from a distance without careful inspection. — 
