General Account of the Ithacan Anura. 11 



Cross and abnormal embraces give us our best clues to the role of 

 size in the mode of approach. In three different instances a captive 

 wood-frog held an Ambystoma in a lumbar embrace. It did not seek 

 the head as did the smaller peeper and swamp cricket-frog. One cross- 

 embrace of a male Rana palustris with a female of the larger species, 

 Rana clamata, displayed several different methods. At first, the male 

 held the female with the right hand dug into the axil, Bufo fashion, 

 and with the left arm and hand reaching around to the middle of 

 the breast, Rana-\ike. Once, it lost its hold and regained a lumbar 

 amplexation. This it kept only a short time, and almost immediately 

 began working slowly through inguinal and axillo-inguinal modes to 

 the axillary type. Another cross-embrace between two other species, 

 namely, between a male Bufo and a female Ra7ia pipiens, proved 

 equally interesting. At first, the toad held the frog with the right arm 

 in front of that of the frog, and with the left arm behind. Later, both 

 arms were behind and they met on the breast, as in males of the genus 

 Rmia. 



Occasionally, in some cross-embraces, when the females proved large, 

 the mating males would seize them from the venter. On April 10, 

 1 908, a male Bufo thus seized a female green-frog. Its arms were behind 

 those of the green-frog and went up on its back. A small male wood- 

 frog with shorter span did the same, except that its arms were ahead of 

 those of the female green-frog. 



Thus, it maj^ be seen that variations are not unusual, and that gener- 

 alizations in this particular must be on numerous records. In the three 

 genera we have observed six or seven modes when normally only three 

 would be expected. Rarely a male displays a gamut of six or seven 

 modes, especially when mating with a female of another species. All 

 these mating phenomena came as an incident to the effort to secure 

 mated pairs for ovulation in captivity. In this way, a positive check 

 was established upon the identification of the eggs laid in nature. 



THE OVULATION. 



It is often asserted that the sexual embrace is continued for several 

 days before ovulation. Such may be the case with individuals mated 

 in captivity, but very few illustrations of it have been found among 

 numerous mated pairs brought in from the field. At the outset the 

 attempt to secure fruitful mating with captive specimens was given up. 

 The few instances where successful show that the intervals between 

 the beginning of the embrace and egg-laying are short. In one case, 

 where a pair of wood-frogs were thus mated in laboratory, ova were 

 deposited 90 minutes after the beginning of the embrace. With two 

 similar pairs of Chorophilus triseriatus, 20 minutes and 90 minutes were 

 respectively recorded. Another such mated pair of Rana palustris laid 

 two days after the beginning of the embrace. 



