32 HELEN DEAN KING. 



during this period that the degree of ripening is supposed to de- 

 termine the sex of the egg." Morgan suggests that the results 

 of Hertwig's later experiments seem to show that the male is 

 responsible for sex-determination. The preponderance of one 

 sex over the other would be explicable on the assumption that 

 " more sperm of one kind, if two kinds exist, are injured or that 

 internal processes may lead to the production of more functional 

 sperm of one sex." It is unfortunate for this suggestion of Mor- 

 gan's that the numerous investigations which have been made of 

 the spermatogenesis of various species of amphibians have so far 

 failed to show the slightest evidence of a dimorphism in the 

 spermatozoa. 



The frog offers much more favorable material than the toad 

 for an investigation of the influence of the ripeness of the egg at 

 the time of fertilization on sex-determination, since it is possible 

 to extend the laying period of a frog over several days while the 

 toad lays all of her eggs within a few hours whether she is sep- 

 arated from the male or not. Two different experiments were 

 made with the eggs of Bufo in order to study this problem. In 

 the first experiment a pair of toads were used that had been 

 brought into the laboratory early in the morning of March 30, 

 1907. The female commenced laying at 10.45 A. M. of the 

 same day. At 11.15 A. M. the toads were disturbed and the 

 eggs already laid (Lot A) were removed to a jar of fresh water. 

 The female began laying again at 12.05 P- M and a second set 

 of eggs (Lot E] were removed at 12.25 P- M. The third laying 

 (Lot C) began about I P. M. and was interrupted at 1.15 P. M.; 

 while the fourth and last lot of eggs (Lot D) were deposited be- 

 tween 2.15 P. M. and 3 P. M. The laying period for this 

 female, therefore, extended over about four hours. Four hun- 

 dred eggs were taken from each lot for the purposes of the ex- 

 periment, each set of eggs being put in a compartment of a large 

 aquarium. The compartments were all approximately of the 

 same size and each contained about the same amount of water 

 and of plant food. All of the 1,600 individuals used in this ex- 

 periment were, therefore, subjected to similar external conditions 

 during the period of their development. There was no appreci- 

 able difference in the rate of growth of the tadpoles in the dii- 



