395 



same limits during early stages as during later ones, proves as far as 

 we can ever hope to prove, that there is no cell division during these 

 periods. No figures of mitosis were observed in the sex-cells of these 

 embryos. The first clear indications of their division are found in 

 embryo 36, which has a c-t length of 10 mm and a carapace length 

 of 6,5 mm, Fig. 2. Some 

 specimens of stages later 

 than this (embryos 37 

 and 43) show no division. 

 We thus see that the 



■'i2^^!?^M2Si"-..^ 



Fig. 1. 



Fig. 2. 



Fig. 1. Chrysemys marginata. An embryo of 2,8 mm total length, the earliest 

 stage considered in this paper. 



Fig. 2. Chrysemys marginata. A specimen in which the length as measured 

 from the cervical bend to the tail bend is 10 mm, while the carapace length is 6,5 mm. 

 At about this stage, the primitive sex-cells begin to multiply. 



Stage at which the sex-cells begin to multiply, varies within pretty 

 wide limits. In these points, the results of the present work are 

 quite in harmony with those of Eigenmann and Beard. 



It will be noticed thai there is great individual variation in the 

 number of sex-cells found in Chrysemys during this period. Id this 

 point, the results of the present work are quite in accord with those 

 of Eigenmann upon Cymatogaster, but wholly out of harmony with 

 Beaed's views. His conception of a specific number of sex-cells ex- 

 pressed by the formula 2° — 1 during these early stages, certainly is 

 not borne out by the facts observed in Chrysemys, in which the number 

 of sex-cells ranges all the way from 302 to 1744. 



It is interesting to note that the small number found in each of 

 the embryos Nos. 18—21, all from the same parent, would seem to 

 show that a certain set of embryos may have a relatively low number 

 of sex-cells, while another set may have a relatively high number. 

 Compare the extremes of this set, 302—528, with the extremes, 

 1082^1740, as shown by embryos Nos. 23 — 27, likewise taken from 

 a common nest. In each case, one finds the other members of the 



