No. 3.] SPERM ATOPH ORES. 363 



Clepsine, — tJie injection of spermatozoa through the body-wall, 

 or hypodermic impregnation, as we may call it. 



This mode of impregnation represents an important economi- 

 cal step in advance of the more primitive mode of setting the 

 seminal elements free in the water. The deposition of sperm- 

 capsules at random on any point of the external surface that 

 happens to be accessible at the moment of meeting, is improved 

 upon by restricting the act to a definite region, as one or more 

 segments of the clitellum in certain annelids, or the surface 

 around the external openings of the oviducts, as in the crayfish ; 

 and, still further, by limitation to the edge of genital pores or 

 seminal receptacles, as in the copepods. The seminal reservoir 

 of the lobster, discovered by Bumpus,^ marks an advance on the 

 conditions obtaining in the crayfish. 



The habit of discharging spermatophores directly into the 

 vaginal orifice, presupposing direct union of the sexual pores, 

 brings us to relations where such copulatory organs as we find 

 in the Gnathobdellidae would become useful. The penis is here 

 only an eversible end-piece of the vasa defercntia — a simple 

 tubular elongation of what in its simplest form would be repre- 

 sented by a pore. 



Lang, who was the first to discover this mode of impregna- 

 tion in the Turbellaria, has thrown out the interesting sugges- 

 tion, that in these animals the penes may have been primarily 

 organs of attack and defence, which assumed secondarily the 

 office of copulatory organs. The grounds for the suggestion 

 may be seen from a citation to be introduced farther on. Such 

 a mode of origin, though it may be true for the Turbellaria, 

 does not invalidate the suggestion I have made for the Gnathob- 

 dellidae, except on the supposition that the penes represent 

 homologous organs in the two groups. Such a supposition 

 appears to be forbidden by the absence of these organs in the 

 lower leeches. It seems to me, therefore, altogether more prob- 

 able that in the higher leeches they have been independently 

 acquired, and that their evolution began after, or simultaneously 

 with, the establishment of the habit of true copulation. 



The structural and ontogenetic resemblances of the penes in 

 the two groups cannot be taken as decisive proof of genetic 

 identity. The resemblances between the penis and the pharynx 



^ The Embryology of the American Lobster. Journ. Morph., Vol. V. [ In press.] 



