74 INTRODUCTION. 



Our larger species of toads and frogs do not 

 appear to be able to propagate until four or five 

 years old. But it has been ascertained on specimens 

 kept in confinement that Alytes, Bombinator, Pelobates, 

 and Hi/la — which are of proportionally larger size 

 immediately after transformation — attain much sooner 

 their full development, and may breed in the third 

 year of their existence. 



A curious fact, for which we can at present find no 

 explanation, is the very considerable excess of males 

 over females in the genera Pelodijtes, Pelobates, and 

 Bufo, when adult at least, as has been observed not 

 only during the breeding season, but also at other 

 times, and especially during the winter, when numbers 

 congregate in holes. In other genera the proportion of 

 both sexes appears about equal ; Born and Yung have 

 even ascertained that in the young of the genus Bana 

 the females are in the proportion of 54 to 61 per cent. 

 It is believed that in some lower animals abundance 

 of food is an important factor determining sex. The 

 two above-mentioned physiologists have conducted a 

 series of experiments on tadpoles of frogs (Bana 

 temporar la), and by giving them a more abundant 

 or more artificial food have obtained a much hio-her 

 ratio of females, viz. 70 to 95 per cent. A. von 

 Griesheim, after examining the sexes of 440 specimens 

 of the common frog captured immediately after the 

 metamorphosis, found only 36 per cent, of males. It 

 would be highly interesting to make a similar investi- 

 gation on the young of some species, such as Bufo 

 vulgaris or Pelobates fuscus, in which the number of 

 adult males far exceeds that of females. 



