STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 215 



those previously obtained when batches of eggs from each uterus 

 of a female were fertilized with sperm from the same male 

 (King, '09), show that if two kinds of eggs are produced in the 

 ovaries of Bufo they must be produced in approximately equal 

 numbers in each ovary. Experiments similar to these can there- 

 fore give no possible clue to the time or to the manner in which 

 sex in Bufo is determined. 



Hertwig ('07) found that the different lots of frog tadpoles 

 that developed from eggs of the same female that were fertilized 

 with sperm from different males showed marked differences in 

 their growth energy. A similar phenomenon was observed in 

 the various lots of tadpoles of Bufo that belonged to this series 

 of experiments. Eggs which were fertilized with sperm from the 

 left testicle of male 2 produced tadpoles which, as a rule, were 

 larger, more uniform in size, and apparently more vigorous than 

 were the individuals in the other lots. The mortality among these 

 individuals was comparatively low. The great majority of the 

 tadpoles that were produced from eggs that were fertilized with 

 sperm from the right testicle of male 3 were somewhat under- 

 sized ; and they were backward in developing, as only 39 of them 

 had completed metamorphosis by June 22. The mortality in 

 this lot was considerable. Both lots of tadpoles derived from 

 eggs that were fertilized with sperm from the right and from 

 the left testicle of male i developed at about the same rate and 

 were of average size. The mortality in these two lots was about 

 10 per cent. 



Owing to a series of accidents a number of individuals in each 

 of these lots were lost; and therefore the comparatively high 

 death rate, as shown in Table II., can be ascribed in great part 

 to this cause. To a similar cause can also be attributed at least 

 10 per cent, of the mortality in the various other series of ex- 

 periments described in the present paper. 



