II HABITS AND NATURAL HISTORY OF THE FROG 51 



the embrace of the male has been investigated by Nussbaum^ 

 in Rana fusca. Females were isolated soon after they came 

 out from their winter quarters, when the eggs were still in 

 the ovary. The eggs were found to leave the ovary, pass 

 down the oviduct, and collect in the uterus as they do under 

 normal conditions. They were not extruded from the uterus 

 all at once as they are in copulation, but were passed out 

 slowly, a few at a time, some eggs often being retained until 

 considerably after the breeding season. In a female killed 

 late in the summer one uterus was found to contain a large 

 amount of jelly, but the eggs themselves had broken down 

 and disappeared. 



Egg laying in Rana esctilenta is apparently more dependent 

 upon external conditions. While R. fusca readily lays its 

 eggs when in captivity, escidenia does so only if the eggs 

 have accumulated in the uteri at the time of capture. 

 When the females are taken earlier, the eggs that are in the 

 ovary are not extruded, but are retained there until they are 

 finally resorbed. 



Proportions of the Sexes. — A male frog, as a rule, pairs 

 with only one female during the breeding season, and it is 

 advantageous to the species that the sexes should be nearly 

 equal in numbers. This relation is, in fact, usually found to 

 obtain among adult frogs. Born,- in studying the proportion 

 of the sexes in young frogs, came to the conclusion that the 

 females often greatly preponderate over the males. In one 

 brood the females were found to constitute ninety-five per 

 cent of the total number. Pfltiger^ and Griesheim,'' who in- 

 vestigated the subject with considerable thoroughness, found 



1 Arch. mik. Anat., Vol. 46, 1895. 



2 Born, Breslauer artzl. Z.eitsck, 1881. 



8 Pfluger, Arch.ges. Phys., Bd. 29, 1882, 

 i Griesheim, Ibid., Bd. 26, 1881. 



