II HABITS AND NATURAL HISTORY OF THE FROG 47 



tion of copulation in frogs kept in the terrarium was found 

 to vary between six and twenty-three days. The less varia- 

 bility of the breeding period in this case is doubtless due to 

 the more uniform conditions under which the animals are 

 kept. The period between the appearance of the first egg 

 mass and the time when all the females have extruded their 

 eggs was found to vary in different localities, between four 

 and twenty-seven days, according to the temperature ; in 

 the terrarium a variation between ten and twenty-eight days 

 was observed. According to Pfliiger, the laying period in 

 Ratia esculenta lasts only two days. It is quite probable 

 that a single copulation extends through the whole breeding 

 season. In Rana fiisca Pfliiger has observed that a male 

 may clasp a female for several weeks, and in Rana esculenta 

 the same observer has recorded an embrace which lasted a 

 month. Steinach records a still longer period for Rana 

 fusca, the pairs remaining united for as much as seven 

 weeks. In these cases the weather was cool, otherwise the 

 discharge of the sexual products would have occurred much 

 more quickly. 



Copulation. — In copulation the male clasps the female 

 just behind her fore legs, where he hangs tightly and main- 

 tains his hold persistently against all efforts to dislodge him. 

 Often the thumbs are interlocked to increase the firmness 

 of his hold. The body of the female is very much com- 

 pressed in consequence of this, but it apparently causes her 

 little inconvenience. The labor of locomotion of the pair 

 falls mainly upon the female, the male exerting himself only 

 occasionally for the maintenance of equilibrium. With the 

 exception of the effort necessary to enable him to retain his 

 hold, the male during copulation is singularly inactive, and 

 will endure unfavorable conditions rather than make any effort 

 to seek a better situation. Sometimes several males will be 



