1922] Phases in the Development of Chrysemys Cinerea 65 



the close of twenty-eight days. Eggs from the same clutch, kept 

 under moist conditions, continued to develop. 



Temperature, of course, plays its part, although a room with a 

 southern exposure gives sufficient heat for reasonably rapid develop- 

 ment. In this connection it was thought desirable to determine the 

 effect of cold upon the rate of development. For this experiment 

 the eggs from turtles No. 128 and No. 129 were placed under the 

 usual incubation conditions except that they were put in a refriger- 

 ator. After a period of about one month one of these was opened 

 and found to be in the blastopore stage, indicating that development 

 does not proceed at temperatures near the freezing point. The. eggs, 

 however, were not injured by the cold, for when placed under the 

 natural heat conditions of the room they began to develop in the 

 normal manner. In order to determine the relative rato of develop- 

 ment, indoors and out, three eggs from each of the specimens No. 

 36, No. 37, and No. 38 were buried in an artificial nest out of doors, 

 exposed to all natural conditions. The remaining eggs from each of 

 these specimens were placed under incubation in the laboratory. From 

 time to time these eggs were opened. Embryo No. 88, fig. 11, was 

 incubated in the laboratory forty-three days, while embryo No. 100, 

 fig. 12, was incubated out of doors in an artificial nest for forty- 

 seven days. Development proved to be about as rapid in the labora- 

 torj'- as outside. 



The presence of soil around the egg is not necessary. This has 

 been tried out in one case with the eggs of the "snapper." Five 

 eggs from a clutch of eleven were placed in a finger bowl without 

 sand or water, (see a, in table below). The remaining six were placed 

 in moist sand, (see b, table below). The two bowls were placed in 

 a glass dish which contained a small quantity of water and cov- 

 ered with a bell jar. Incubation was allowed to go on for a few 

 days and then the eggs were opened with the following results : 



(a) 5 eggs — 3 embryos, 1 dead, 1 egg infertile. 



(b) 6 eggs — 3 embryos, 1 dead, 2 eggs infertile. 



Although the eggs develop without soil, nevertheless, it serves the 

 useful purpose of holding the eggs in position during development. 

 The rate of development of the uterine egg is about the same as 

 that of the laid egg. An examination of the drawings of embryo No. 

 68, fig. 34, which was incubated twenty days, and of embryo No. 



