OCR Text |
Show 1901.] FROM BRITISH EAST AFRICA. 339 Polytoreutus. The two glands open on to the exterior by a median bursa copulatrix of circular outline, which of course underlies the nerve-cord and the end of the spermathecal sac. A more careful examination of the spermiducal glands shows that they can, like those of Polytoreutus gregorianus for example, be divided quite plainly into two regions. The "'elbow," already mentioned, marks the boundary-line between these two regions. The proximal part of the gland, i. e. that which is nearest to the orifice into the bursa copulatrix, is perhaps one half of the length of the rest. It is oval in form and gradually tapers to a slender tube, which opens into the bursa copulatrix. At the very extremity of the latter, just before its orifice into the bursa, opens the sperm-duct, which is here as elsewhere covered with a thick layer of muscular fibres which dilate the duct to twice the diameter it would have were there no muscular coat, and, of course, thus accounts for its prominence in dissections. The distal part of the spermiducal gland has not the lateral diverticula that occur in Polytoreutus ccsruleus, according to Michael sen's figures and descriptions *; but it presents some hint of this in a series of irregularly disposed bulgings of the wall of the tube. The bursa copulatrix appears to have a circular contour; but when the upper part into which the spermiducal glands open is pushed aside it is seen to communicate with the exterior by a curved peduncle, so that on a lateral view it appears almost pear-shaped. The spermathecal sac is like that of several species, including P. kilindinensis and P.finni, in that it has but two diverticula. The median part of the sac is very wide anteriorly and gradually shrinks in diameter until-where it traverses the bursa copulatrix- it is of quite small diameter; from the anterior end two relatively huge lateral sacs are given off, one on each side. These reach back to nearly the point of external opening of the sac. From the underside of each of these, quite hidden until the diverticulum is lifted up, arises the tube communicating with the egg-sac and the oviduct, the arrangement of which parts is as in other species of the o-enus, there being also a representative of what Michaelsen has termed the "Samenkiimmerchen " in Polytoreutus cceruleus, &c. This seminal chamber is a very extraordinary formation. In the specimen which I examined there was but one instead of the four figured in Polytoreutus cceruleus by Michaelsen. The single chamber wks choked by a mass of ripe spermatozoa (as I interpret the structure in accord with Michaelsen), the tails of which depended into the lumen of the oviduct, while their heads were apparently fixed in the epithelium of the chamber ; this recalls the case of the spermathecal diverticula of many Megascolicidse, where, as I first showed2, the spermatozoa are confined to the diverticula and are there attached to certain glandular cells. 1 " Beschreibung der von Herrn Dr. Franz Stuhlmann im Mundungsgebiet des Sambesi gesammelten Terrieolen," JB. Hamb. wiss. Anst. vii. pi. i. fig. 10, n 24. s " O n the Specific Characters, &c. of certain New Zealand Earthworms," P.Z.S. 1885, p. 830. |