SEX-DETERMINATION IN AMPHIBIANS ozo 
in order that the result of these experiments may be ascribed to 
selective fertilization. 
There remains the possibility that the sex ratios in these lots 
of individuals were chance variations in the normal sex ratio, 
and that the treatment to which the eggs were subjected, previous 
to their fertilization, had nothing whatever to do with the sex of 
the future embryos. In table 2 is given a summary of the pro- 
portion of the sexes and of the sex ratios in various lots of indi- 
viduals that have served as controls for different series of experi- 
ments made during the past six years. The 500 young toads 
examined in 1904 were obtained from the banks of the Susque- 
hanna River at Owego, New York, shortly after they had com- 
pleted their metamorphosis under natural conditions. All of the 
other individuals used in computing the table were developed 
from the eggs of females obtained in the vicinity of Philadel- 
phia, Pa. In every case the eggs were normally or artificially 
fertilized in laboratory tap water, and the tadpoles reared under 
very uniform external conditions. No lots of individuals have 
been included which developed from eggs that were subjected to 
any abnormal treatment, at or before the time of fertilization, 
TABLE 2 
Sex ratios in various control lots of individuals 
yeag | OF | acemenacran | (Mates | tuMtared | VU ruene Sup cine 
1904 500) 241 | 259) ates 7) 93.05 
00% I | °259 | 341 ie os6 33 75.92 
| | 651 292 359 554) 1) | 81.38 
1908 140 | 64 76 54.28 | 84.21 
1909 S230) ci) 157) | seiGomaeemolesS 94.56 
210° 134 65. | 69 | 51.41 | 94:20 
cate 1259 aia | - 372 || “408 52.00 | 92.25 
201 TAO 8 565 75 53.57 86.66 
200i) 2794 , eats 53700, |; 188.67 
er S50 men mene S22 169 153 47.50 | 110.45 
350 334 178 | 156 | 46.40 | 4114.10 
Total 4119 | 1956 21638 Ml 52-51, — |), 90-42 
