66 Journal of the Mitchell Society [September 



69, fig. 37, incubated seventeen clays, shows that the latter, which is 

 from a laid egg, is slightly more in advance, as would be expected. 

 Comparison of embryo No. 92, fig. 10, and No. 99, fig. 13, shows that 

 the former, which is from a uterine egg, is more advanced. In this 

 case, also, the laid egg was incubated three days longer than the 

 uterine egg. 



Even among uterine eggs there is a variation in the rate of de- 

 velopment. Two eggs were placed under identical incubation condi- 

 tions, one day apart, and Avere opened on the same day. From these 

 embryos No. 80, fig. 39, and No. 81, fig. 38, were obtained. Embryo 

 No. 80 is considerably more developed than No. 81 would be if it 

 had been incubated for the same time. Such difference may pos- 

 sibly be due, in some degree, to the extent of the egg development 

 in the uterus, but more likely it is due to the different developmental 

 rates. 



Altogether one hundred and sixty-seven eggs were incubated the 

 first year. From these one hundred and ten embryos, or slightly 

 over sixty-six per cent, developed. During the second summer, three 

 hundred and five eggs were handled from thirty-five clutches. Since 

 a number of these clutches were taken from turtles collected before 

 the spring copulation season began, there is a rather high percentage 

 of infertility, some ten clutches failing to have any eggs develop. 



The ease with which turtles may be secured and incubation car- 

 ried on, and the high percentage of fertility, make the turtle an excel- 

 lent subject for embryological work. 



Preparation of Material 



Some of the eggs collected were opened immediately and some 

 were artificially incubated according to the method just described. 

 The embryos were all killed in Bouin 's fluid, stained in Alum Cochineal 

 in toto and sectioned in paraffine. In this manner some two hun- 

 dred and forty embryos have been prepared for study. 



Development History Through Gastrulation 



As stated earlier in this paper, many of the eggs studied were 

 removed from the oviduct and artificially inc'ul)ated. No fertilization 

 stages were found. 



