THE BREEDING SEASON 19 



when the winter sets in, having passed the summer in the best 

 circumstances in regard to light, heat, and supply of food. Bles's 

 observations relate more especially to the African frog, Xenopus 

 Icevis, but he believes his conclusions to apply in a large degree to 

 many other species of Amphibia. 



The frogs in question were kept in a " tropical aquarium " (that 

 is to say, an aquarium which could be kept at a tropical temperature 

 by regulating a heating apparatus). In the summer the temperature 

 was maintained at about 25 C. ; in December 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 

 190M, 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 



o / / o 



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, described in the 

 next chapters.) The male Xenopus 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 T it would appear that Xenopus, in its native 



1 Leslie, " Notes on the Habits and Oviposition of Xenopus l<xvis" Proc. 

 Zool. Soc., 1890. 



