368 WILLIAMS : ON THE GONADS OF THE LIMN^A. 



hermaphrodite duct runs a sinuous course through the substance 

 of that digestive gland to get into relation with the albumini- 

 parous gland when it becomes very convoluted so as to simulate 

 a gland-like mass between that organ and its accessory gland. 

 The common generative canal is ribbon-shaped. 



From the consideration of the discrete positions of the male 

 and female genital apertures in both these species it will thus be 

 seen how that two cannot engage in coitus in such a complete 

 manner as occurs in the Helices ; how it is that fecundation of 

 all the animals engaged in coition at any one time cannot take 

 place at one and the same time ; how it is, in fact, that we 

 find Z. peregra~zs, was first observed by Prevost — banded 

 together in threes, or sometimes in greater numbers, the one 

 fecundating the other. In L. stagnalis, as two are the number 

 generally seen together in coitus at the same time, impregnation 

 of only one of them, at one time, can occur, unless the animals 

 are placed in opposite directions one to the other. In L. peregra, 

 taking the three engaged from above downwards, it will be 

 noticed that the general condition of affairs is that the penis of 

 the first is exserted into the vagina of the second, and that it is 

 not fecundated at all itself but is fecundating, that the second is 

 being fecundated by the first and is fecundating the third, and 

 that the third is being fecundated but is not fecundating. So 

 that of three peregras banded together for fecundating purposes, 

 two only of them are fecundated, the second and the third, and 

 two only are fecundating, the first and the second. The exserted 

 penis in both the species is flattened and triangular in shape. In 

 L. stagnalis during coition — this being the only species I was 

 fortunate enough to kill with the penis exserted — I find the 

 relative positions of the organs inside the animal changed to but 

 some slight extent. The penis, of course, is absent, and its 

 place is occupied by convolutions of the vas deferens, the 

 terminal portion of which runs through the centre of the ex- 

 serted penis and opens by a foramen or meatus at its extremity 

 in order for the ready conveyance of the spermatozoa into the 

 vagina of the one being fecundated. 



J.C, v., Oct., 1888. 



