330 ANIMAL PAEASITES. 



and the walls of the sheath appear to coalesce with the wall 

 of the cloaca just mentioned. The elastic sheath of the penis, 

 formed, as already remarked, of elastic bands, by its contractility 

 enables the penis to project or retreat into the cloaca. It appears 

 to me to be most probable that during coition the infundibuli- 

 form root of the penis itself is pushed forward to the point at 

 which the above-mentioned elastic envelope of the penis opens 

 into the cloaca, and at this point takes up the seminal filaments 

 or globules, which are then conducted forward to the vagina in 

 the furrow of the penis. The kind of mechanism by which the 

 transfer of the seminal globules to the female vagina is effected 

 has already been referred to. 



In the act of copulation, the male is assisted not only by the 

 possibility of bending his caudal extremity into a semicircular 

 form, and thus embracing the female, but also by the existence 

 at the very extremity of the cloaca, of a cylindrical protrusible 

 and retractile appendage, which is certainly intended to enter the 

 vagina. This appendage (bursa, gaine renflee ou vesiculeuse of 

 authors) forms a tube, the basal substance of which is the general 

 skin of the body. On its surface it possesses small warts or 

 spines, which have already been mentioned under the general in- 

 tegument, which have their points directed upwards and outwards, 

 and certainly assist in the fixation of the male in the vagina of the 

 female during copulation, and remain longest upon this part of 

 the body without falling off, because this tube itself being re- 

 tractile within the abdomen of the male, and on the whole but 

 rarely used, is less exposed to mechanical injury or friction 

 from without. This appendage, moreover, has several excisions 

 at its extremity, by which the whole acquires an appearance as 

 though it were composed of several branches, which separate in 

 a gaping manner at their free end. I can compare this appear- 

 ance with nothing better than with that of the anterior extremity 

 of an expanded uterine speculum with several arms. The number 

 of branches formed by these tubes, is not so easily ascertained; 

 there are certainly three, if not four, which I have several times 

 thought I counted. By this structure also the act of copulation 

 itself is essentially assisted and facilitated. Thus, in the 

 first place, the free ends of the tube must lie together in the 

 form of a cone, and open the somewhat thick-walled rigid 

 vagina. As soon as the tube enters the vagina, the branches 

 probably separate ; and, as it were, throw themselves outwards, 



