OF NORTH AMERICA. 45 



when equal quantities of both species were placed in the aquarium, 

 they chose the latter species first. 



j. REPRODUCTION AND NIDIFICATION. 



The Lymnseas are sexually hermaphrod : tes. Unlike the helices, 

 they are capable of mutual union, each playing the part of male to 

 the other. This is possible owing to the wide separation of the male 

 and female orifices. Not only may two individuals perform the act 

 of copulation at the same time but three or more individuals have 

 been observed in coitu, one individual performing the part of both 

 male and female with two other Lymnseas. 



That Lymnsea is capable to some extent of self impregnation is 

 apparently proven by Braun 3 who isolated Radix auric ularia when 

 hatched. One year later each of three isolated individuals produced 

 respectively one, four and five egg masses, several of which hatched 

 out young auricularias. 



The copulation of Lymnaa stagnalis lilliana was recently ob- 

 served and the following notes were made: The penis-sac is everted 

 its whole length and appears as a very large, flat, elongate-triangular 

 organ. When in coitu the male organ is firmly attached to the female, 

 requiring a very strong pull to dislodge it. During the orgasm regular 

 pulsations may be seen following the course of the vas deferens, the 

 penis-sac being so transparent that this organ may be plainly seen 

 occupying a long loop, folded longitudinally. The penis-sac is much 

 more swollen during copulation than when observed in a dissected ani- 

 mal. During coition the male remains quiescent, with tentacles drawn 

 inward and head much contracted. The female, 4 however, seemingly 

 pays little attention to the operation, but crawls about eating or exam- 

 ining the surroundings with her tentacles. When pulled apart and 

 separated, the male immediately seeks the female again, if in the vicin- 

 ity, or if placed near another individual, proceeds to search for the 

 female opening at the base of the neck. The male is frequently 

 found on the shell of the female. 



Lymncea stagnalis lilliana, Galba emarginata and Galba lanceata 

 have been observed copulating, and, curiously enough, emarginata, 

 though a much larger animal, tried several times to copulate with 

 lanceata, showing that at this period (the last of August) the sexual 

 instinct is so strong that even distinction between species is lost. This 

 was also observed to be the case with stagnalis and emarginata. 



3 Nach. Deutsch. Mai. Gesell., XV, p. 146. 



4 The terms male and female are here used simply to identify the imme- 

 diate sex individuals, as Lymnaea is hermaphroditic, carrying the organs of 

 both sexes in the body, as already explained. 



