STUDIES ON SEX-DETERMINATIOX IN AMPHIBIANS. 213 



tween the two lots in which the eggs had been fertilized with 

 sperm from the right and from the left testicle of the same indi- 

 vidual (male i). Variations in the percentages of females as 

 great as those shown in the above table have been obtained in 

 other cases where batches of eggs from the same female were 

 fertilized with sperm from the same male (Table I.)- The 

 results of this experiment, therefore, give no very definite support 

 to Morgan's contention that the male is probably the sex de- 

 termining factor in amphibians as it appears to be in some of 

 the lower forms. On the other hand, the experiment proves 

 nothing against this theory. For a comparison of the percent- 

 ages of females in the lot of individuals produced from eggs that 

 were fertilized with sperm from the left testicle of male I with 

 that of the corresponding lot in which sperm from the left testicle 

 of male 2 was used show r s a difference of but 4.88 per cent.; in 

 the two instances in which sperm from the right testicle was used 

 to fertilize the eggs, the difference in the percentages of females 

 among the young toads is 3.86 per cent.; where one lot of eggs 

 was fertilized with sperm from the right testicle and another lot 

 with sperm from the left testicle of the same individual, there 

 is later a difference of but 4.17 per cent, in the percentages of 

 females in the two lots. It seems evident, therefore, that both 

 kinds of spermatozoa, if two kinds exist, must be produced in 

 approximately equal numbers in each testicle of every male. 

 On the theory that the male is the sex-determining factor in 

 amphibians one would therefore expect to find practically equal 

 proportions of the sexes in any large lot of individuals, whether 

 the eggs had been fertilized with sperm from the same or from 

 different males. 



The view that males are produced by the fertilization of eggs 

 with spermatozoa from the right testicle, while females result 

 if eggs are fertilized w r ith spermatozoa from the left testicle 

 has recently been advocated by Von Seligson ('950, '95&). This 

 theory, which is generally credited to Hippocrates (460-377 B.C.), 

 is not adequate to explain the determination of sex in Bufo 

 since, as shown in the above table, males and females are pro- 

 duced in approximately equal numbers when lots of eggs from 

 the same female are fertilized with sperm from the right or from 

 the left testicle of the same individual. 



