No. I.] SPHYRANURA OSLERl. 4 1 



Zeller had given such a detailed account of the process of 

 sexual union, and of the copulatory cushions and lateral vaginae 

 in Polystonimn integerrimum, and structures of so entirely simi- 

 lar a character had been described by the senior author in P. 

 oblongiim, from the musk-turtle, that we were prepared to find 

 similar conditions in Sphyranura. Here, however, no lateral 

 vaginae exist, or rather they are only represented by the two 

 receptacula seminis, and the ducts which lead from them to the 

 central ootype. The sperm with which these receptacles are 

 generally packed is consequently introduced through the genital 

 sinus, and inwards to the ootype through the uterine tract of the 

 oviduct, the direction of the ciliary movement in which must 

 favor its inward passage. We at first observed that the invest- 

 ing membrane was often incomplete in sections opposite the 

 receptacula, and supposed that this pointed to the existence of 

 a direct communication with the outside ; but repeated attempts 

 to demonstrate the existence of such apertures failed, both with 

 fresh and preserved specimens, so that we concluded that the 

 fragility of the wall of the body there was owing to the disten- 

 tion of the underlying cavity. 



We conclude that these receptacula, whose walls are muscular 

 and under control of certain large isolated ganglion-cells similar 

 to those which we have spoken of in connection with the con- 

 tractile bladders of the excretory system, serve as reservoirs of 

 sperm which is introduced through the genital aperture before 

 the uterine cavity is occupied by a mature egg, and is dis- 

 charged thence as the ripening of the eggs demands. What 

 the source of the sperm in the receptacula is we are unable to 

 say; we have never seen any individuals in copula; and it 

 is obvious, from Fig. 16, that self-impregnation would be ren- 

 dered quite possible by the simple closure of the aperture 

 of the genital sinus. 



Fertilization takes place, not in the ootype, but within the 

 ovary itself. We have frequently observed spermatozoids be- 

 tween the ripe egg and the ovarian wall, and, indeed, have 

 detected in the ripe egg a male pronucleus, with the surround- 

 ing disturbance of the cytoplasma. Some cases of polyspermy 

 were likewise noted ; but we have never seen segmentation taking 

 place, and conclude that the egg leaves the ovary for the uterus 

 on the completion of the act of fertilization. 



