STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 



33 



ferent compartments and the mortality was nearly the same in 

 each lot. The results of this experiment are summarized in the 



following table. 



TABLE II. 



The results of this experiment show a striking uniformity since 

 in all four lots about the same proportion of the individuals in which 

 sex was ascertained were females. The excess of females was slightly 

 greater in the two middle lots (Band C) than in Lots A and D. This 

 result would seem to support Hertwig's contention that eggs in 

 the middle phase of ripening at the time of fertilization tend to 

 produce a greater proportion of females. The extreme lots of the 

 series (A and D} did not, however, give a correspondingly greater 

 proportion of males as the theory demands. It is very probable, 

 therefore, that the slightly greater proportion of females in the 

 two middle lots has no especial significance. The comparatively 

 short interval between the laying of the eggs in Lot A and of those 

 in Lot D makes no direct comparison possible between the re- 

 sults of this experiment and those of Hertwig on Rana, since in 

 some of Hertwig's experiments there was an interval of two or 

 three days between the laying of the different lots of eggs by the 

 same female. Normally the eggs of the frog, as well as those 

 of the toad, are all laid within a short period of time. It would 

 seem, therefore, as if in the above experiment a relatively greater 

 number of males should have developed from the eggs of Lots 

 A and D if, as Hertwig believes, the ripeness of an egg at the 

 time of fertilization has any influence on its sex and if eggs ferti- 

 lized in early or in late phases of ripening have a tendency 

 towards male production. 



All of the eggs used in this experiment should have been 

 peculiarly favorable for the production of males according to 

 Hertwig's theory, since, owing to the very early spring in 1907, 



