MIGRATION AND SEX RECOGNITION IN FROGS 337 



that "the color of the female may possibly be a factor and that 

 the behavior of the female is probably a factor in sex recognition." 

 While Banta notes that the usual procedure is the indiscriminate 

 testing of many individuals regardless of their sex, he neverthe- 

 ess postulates a precopulatory recognition established through 

 sensory channels. This writer does not attribute any signifi- 

 cance to the postcopulatory reactions of clasped frogs; in fact, 

 he finds no consistent difference in the resistance of the two 

 sexes when clasped. Miller ('09), on the other hand, finds in 

 toads that "males cannot distinguish at sight males from females. 

 For this reason they are continually clasping one another. They 

 have a call of three or four notes which they utter in rapid suc- 

 cession when taken up between the finger and thumb, or clasped 

 by another male. This seems to be a warning signal, for a male 

 will release another as soon as he chirps." In an effort to obtain 

 evidence on sex recognition, the writer observed mating reactions 

 in the wood frog and leopard frog, both under natural condi- 

 tions in the pond and under experimental conditions in terraria 

 In both species, pursuit under natural conditions did not 

 differ whether the frog pursued was male or female. In this 

 respect the observations are contrary to those of Banta, who states 

 that "The beginning of the attempt of a male upon a female is of 

 course not in any way different from his approach toward another 

 male, but when he actually touches or often only nears the female 

 his actions are usually very different, for instead of the vigor 

 and aggressiveness of the assailant rapidly falling off, as in the 

 case of one male approaching another, the aggressiveness is 

 tremendously increased." In practically every instance none 

 but moving frogs were pursued, although at a distance of a foot 

 or less a quiet frog might be attacked, and a quiet frog if touched 

 by a male usually was attacked, in both cases regardless of sex. 

 A male upon which clasping was attempted sometimes only 

 croaked when touched; if the attempt to clasp him were con- 

 tinued, violent struggles, croaking, and inflation of the vocal 

 sacs were followed by dislodgment of the clasping male. Fe- 

 males when clasped were occasionally passive, sometimes strug- 

 gled very vigorously, and sometimes struggled only a little. 



