MIGRATION AND SEX RECOGNITION IN FROGS 341 



and on the day of the experiment only few pairs were seen in 

 the pond, while numerous single individuals were noted. The 

 necessity of a visual factor was eliminated by no. 6, where correct 

 coupling occurred in the dark. The efforts of clasping frogs 

 were not confined to their own species, or even to frogs, as no. 

 5 and no. 10 indicate. Holmes ('12) shows that these extraspe- 

 cific claspings are even more extensive. 



The variation in resistance offered by females may be tenta- 

 tively explained by a gradual development of the physiological 

 state favorable for clasping. Passive acceptance of the clasping 

 male may be associated with the optimum development of this 

 state, while resistance may indicate that the female is not yet 

 ready or perhaps has already undergone the climax. In the 

 same manner, there may be a gradual development of the clasp- 

 ing iiripulse in the male, for under natural conditions it is lost 

 after the termination of the breeding season. The less persistent 

 efforts to maintain a hold may be associated with a small degree 

 of development of the impulse. And the ardor which results 

 in the clasping and retention of the clasp on females, disabled 

 males, salamanders, frogs of other species, etc., may be associ- 

 ated with the maximum development of the impulse. 



Now, if males attempt clasping with both sexes of their own 

 species, with other animals and objects, it seems that sight 

 plays no part except to inform the male that there is something 

 to be clasped. In the light of extraspecific pairing (no. 5 and 

 no. 10), it seems absurd to attribute any role ot sight in sex recog- 

 nition, either on a basis of color or behavior. That sight is not 

 even essential, that other stimuli are responsible for correct 

 coupling, was shown by no. 6. 



It has been pointed out that females will sometimes resist 

 when clasped by males, that normal males always resist. Too, 

 it was shown that following the resistance of the female the male 

 might or might not continue his efforts, while in the case of 

 males he did not persist. The resistance of the males consisted 

 not only in struggling, but also in the inflation of the vocal sacs 

 and croaking; in fact, attacked males did at times cause the 

 desistance of the attacking males by only croaking when they 



