8 



General Account of the Ithacan Anura. 



quiet female and also to its more sun-exposed position when mated. 

 In the toads which lay in the shallows, the difference in color is not so 

 noticeable nor is it in the night-laying tree-toads. In the peeper and 

 the swamp cricket-frog, however, which lay by day as well as at night, 

 the males are usually darker. In these tree-frogs, as in the toad, the 

 males are distinguished by a viscid subgular pouch which in some forms 

 may help the male to retain his hold of the female. In addition, the 

 male toad has the first two fingers with horny excrescences. 



THE CUSTOMARY AMPLEXATION. 



In all our eight Anura the embrace is behind or above the arms. 

 In the five species of Rana it is usually pectoral, the hands appressed 

 to the breast of the female; while in the two species of Hyla and in Bufo 

 the hands of the male, with fingers folded back, are dug into the axils 

 (axillary) or just above the axils (supra-axillary) of the female. 



CROSS-EMBRACES. 



The possibility of hybrids makes this phenomenon extremely inter- 

 esting. Pairing between different species of Anura is quite frequently 

 noted in captivity, though our usual isolation of each species did not 

 give ample chance for it. Inasmuch as the mating occurred in cap- 

 tivity, no ovulation was expected, nor was it recorded in the instances 

 which follow : 



Males. 



Rana sylvatica 

 Rana sylvatica 

 Rana pipiens 

 Rana pipiens 

 Rana pipiens 

 Rana pipiens 

 Rana palustris 

 Rana palustris 

 Rana palustris 



Females. 



X Rana palustris. 

 X Rana clamata. 

 X Rana palustris. 

 X Rana clamata. 

 X Rana sylvatica. 

 X Bufo 1. americanus. 

 X Rana pipiens. 

 X Rana clamata. 

 X Bufo 1. americanus. 



Males. 



Rana clamata 

 Rana clamata 

 Rana clamata 

 Bufo 1. americanus 

 Bufo 1. americanus 

 Bufo 1. americanus 

 Hyla pickeringii 

 Hyla pickeringii 



Females. 



X Rana pipiens. 



X Rana palustris. 



X Rana sylvatica. 



X Rana pipiens. 



X Rana clamata. 



X Rana palustris. 



X Rana sylvatica. 



X Chorophilus triseriatus. 



We have long suspected that when two species were vigorously mating 

 and ovulating in the same area, embraces between the two might occur. 

 In 1911 especial attention was given to this matter, and records of this 

 sort were made in two different localities. On the same day (April 

 28, 1911) a male Rana pipiens mated with a female toad, and a male 

 Rana pipiens with a female Rana palustris (Plate iv, Fig. 2). In each 

 case, the individuals of the species concerned were very numerous and 

 ovulating in the same space. In the solitary species there is not the 

 strong inclination nor the chance for cross-embraces that there is in 

 these abundant gregarious forms with overlapping or coincident breed- 

 ing seasons and kindred places for ovulation. 



