OCR Text |
Show L901.] FROM BBITISH EAST AFRICA. 349 Lumbricida;. The head-end is in several respects reminiscent of the corresponding region of the spermatophore of Tubifex rivu-lorum. There is a terminal beak, which is followed by a thick collar, after which tbe-at this part narrow-spermatophore gradually widens out into the bag-like posterior region. The spermatophores are so bulky that there is only room for two in the large spermathecal sac ; at least I have not seen more than two, though the sac might accommodate perhaps three with some little difficulty. In every case the mouth of the spermathecal sac was plugged with one spermatophore, while another lay further up the sac and not in contact with the first spermatophore. Lankester, as I have already mentioned, found in Tubifex rivulorum that the head of the spermatophore was moulded by the terminal part of the spermatheca ; he proved this not merely by the correspondence in form, but by the actual occurrence of a spermatophore with the projections of the head fitting into the lateral depressions of the spermatheca. I find precisely the same thing in these spermatophores of Stuhlmannia. The wing-like processes of the head fit into concavities and on to convexities on the walls of the spermathecal sac with great accuracy, while the beak-like anterior termination of the spermatophore corresponds to the narrow terminal duct of the sperm-receptacle. There can be, therefore, in m y opinion, but little doubt that this part of the spermatophore at least is moulded by tbe form of the spermathecal sac. The rest of the spermatophore also shows evidence of being moulded by the spermathecal sac. The sac is narrower at first and then widens out. In the same way the spermatophore is narrower at first and afterwards becomes broader. Its diameter is throughout not far short of the sac in which it lies. The only alternative locality for the formation of the spermatophore in Stuhlmannia is the spermiducal gland, or possibly the unpaired muscular sac which opens on to the exterior in relation to the spermiducal glands. But the lumen of neither of these organs has anything like the requisite breadth for the inclusion of the fully formed spermatophore, which cannot therefore, so far as I can see, be possibly moulded in its entirety anywhere save in the spermathecal sac. This, however, is not tantamount to saying that the spermatophore is altogether formed in the spermathecal sac. But before discussing the actual place of its origin, the rest of its structure must be dealt with. The walls of the spermatophore are much thicker at the collar region than elsewhere : in front of the collar the thin and narrow beak has thin walls, and is widely open at the end. This, it must be remembered, is the end which is turned towards, and indeed is not far from, the external orifice of the spermathecal sac. In examining closely with a high power the end of the spermatophore, I observed a stream of spermatozoa which had evidently issued from the open mouth. W h y this apparent waste takes place I do not know, but that it must under normal circumstances take place is clear from the width of the mouth, which is not narrow enough to keep the active |