THE BREEDING SEASON 21 



it was allowed to drop to 15 16 C. during the day, and 

 5-8 C. during the night. The bottom of the aquarium was 

 covered with earth and stones, on which the weed Vallisneria 

 thrived. The water in the aquarium was never changed. The 

 frogs were fed daily upon small worms, or strips of liver, until 

 they would eat no more. During winter they became lethargic, 

 taking very little food. When the temperature rose in the 

 spring and the days became brighter, the frogs became more 

 active, especially the males. At this time breeding could be 

 induced by a certain method of procedure which Bles describes 

 as follows : " First, the temperature of the aquarium is raised 

 to 22 C. ; and secondly, when it has become constant, a certain 

 amount of water, say two gallons, is drawn off morning and 

 evening, allowed to cool for twelve hours, and then run in 

 slowly in the following manner, in order to simulate the fall of 

 rain. The cooling vessel is raised above the level of the 

 aquarium, and a syphon is used to run off the water. The lower 

 end of the syphon is drawn out to a fine point, and turned up 

 in such a way that the water rises up like from a fountain, and 

 falls as spray into the aquarium. ... By carrying out such 

 measures I obtained from one female, between April and July 

 1903, more than fifteen thousand eggs/' 



The abdomen of the female Xenopus is stated to become very 

 much distended during the winter by the enormously enlarged 

 ovaries. " The three flaps surrounding the cloacal aperture are 

 flaccid until the spring, when they become swollen and turgid, 

 and more highly vascularised." (Cf. the changes in the female 

 genital organs of Mammals during the " heat " periods, de- 

 scribed in the next chapters.) The male Xenopm is said to 

 assume its nuptial characters two days after the temperature 

 is raised to 22 C., and a very little later it becomes vocal, the 

 voice strengthening from day^to day. Copulation takes place 

 only at night, and spawning may commence an hour afterwards ; 

 but this does not occur unless the water is changed in the manner 

 above described. 



According to Leslie l it would appear that Xenopus, in its 

 native country, breeds only in August, i.e. in the South African 



1 Leslie, "Notes on the Habits and Oviposition of Xenopus Icevis," Proc. 

 Zool. Soc., 1890. 



