MIGRATION AND SEX RECOGNITION IN FROGS 339 



a little difficulty in gaining a hold upon so large a mate, but as she did 

 not oppose his efforts, succeeded. The clasp continued for eight days. 



6. Wood frog, April 1st. At 4 p.m. on this date five males and three 

 females were placed together in a light-proof container. At 8 a.m. of 

 the next day the container was opened, and all three females were 

 found clasped by males. In the interval, especially at first, croaking 

 was heard within the container. 



7. Wood frog, April 1st. In a terrarium containing a number of this 

 species one male clasped another. The clasped male resisted, turning 

 on his back and croaking loudly. After a half minute the clasping 

 male loosed his hold. 



8. Leopard frog, March 30th. Two males which had not been clasp- 

 ing and one male from a pair were placed in a terrarium with a female 

 from a pair. One of the males obtained a clasp on the female, but 

 she struggled so violently as to succeed in dislodging the male. 



9. Wood frog, March 31st. A female was introduced into a terrarium 

 containing two clasping pairs and three single males. Within ten 

 minutes one of the males tried to mount her; he approached from her 

 left side, but she pushed him back with her fore leg. He persisted in 

 attempting to mount, and after three minutes her resistance became 

 more marked — jumping about and turning the ventral surface upward. 

 In spite of this opposition, the male grasped her; within seven minutes 

 he secured the usual clasp and remained. 



10. Wood frog^ and Ambystoma, April 1st. Three single males and 

 two females which had not been pairing and a clasping pair were 

 placed in a terrarium with a female Ambystoma punctatum. The 

 terrarium contained no water, only damp leaves and grass at the 

 bottom. In a few minutes two males clasped the salamander, both 

 with their heads directed toward her posterior end, one of them clasp- 

 ing her head and the other her body a Httle behind the forelegs. In 

 nine minutes the third male clasped the salamander midway between 

 the two pairs of legs. All three held tightly. When she tried to dis- 

 lodge them their clasp tightened and their hind legs were braced 

 against the body of the salamander. In forty-five minutes the third 

 male dropped off, but in twelve minutes returned and secured a clasp 

 in approximately the same position as before; he kept his vocal sacs 

 inflated and croaked repeatedly. After two or three minutes he let 

 go, the salamander writhing and struggling. At 1:05 p.m. the male 

 which had clasped her head let go, and at 9 p.m. the one clasping back 

 of her fore legs did likewise. During the last hours of clasping the 

 salamander lay quietly. 



11. Leopard frog, March 30th. On the evening of March 30th seven- 

 teen females and twelve males were placed in a terrarium, rather 

 closely crowded. After an elapse of twelve hours there was only one 

 clasping pair. 



13. Leopard frog, March 31st. Two single males, a single female, 

 and the male and female separated from their clasp were placed in a 

 terrarium at 9:15 a.m. At 10:45 both females were clasped; at this 



