| OCR Text |
Show 140 DR. W. B. BENHAM ON [Feb. 16, by dissection, controlled by examination of a series of longitudinal sections. A single pair of testes lies in somite x. enclosed with the ciliated rosettes in a special sac, continuous below the gut from side to side, and with the sperm-sacs in the following somite ; of the latter there is but one pair in the specimen examined-which, it must be remembered, may not have been quite mature ; they do not extend into either of the neighbouring somites, but are entirely contained in somite xi. (Plate VII. fig. 3, sp. sac). [In P. heteroporus, Perrier places the " testicules," i. e. sperm-sacs, in somite xii.] The sperm-ducts were traceable to somite xviii., in which lies a pair of prostates (Prost., fig. 3). Each prostate is cylindrical, and curved upwards, so that the free end, which is slightly recurved, lies above the gut, the ventral end is continued as a narrow muscular duct (gen, d.) along the body-wall to the external pore ; this " genital" or penial duct receives the sperm-duct immediately after its origin from the glandular portion of the organ. The prostates are entirely confined to their somite, and their histological structure agrees with that of Perichceta and other worms. [In P. heteroporus the gland is several times bent, as in Acanthodrilus, and is wider ventrally, where the penial duct originates.] A pair of ovaries lies in somite xiii. (Plate VII. fig. 3, ov.), and the oviducts have the usual position. The gonad is fairly large, and in section is seen to occupy the greater part of the cavity of the somite, extending upwards and outwards on each side. I may again remark that I find no structures in somite x. which would answer to Perrier's "ovaries"; indeed, he himself felt uncertain as to the correctness of his interpretation of these grape-like glands, and suggested that they might be an anterior pair of " testicules " (sperm-sacs). He remarks, however, that their structure differs from that of the sperm-sacs in somite xii. and states (on p. 259): " Ce sont des grosses granulations refringentes, groupees de maniere a constituer des spheres, au centre desquelles nous avons vu souvent une apparence de vesicule transparente et des laches germinatives," but adds his doubt on the matter of interpretation which I have quoted above; there is, indeed, nothing in his description which leads me to believe that these structures are ovaries, and when he mentions that a large funnel, like that of the sperm-duct, lies below this organ-i. e. in the position in which I find the ciliated rosettes-I think we may conclude that these organs, whatever they may be, are not ovaries. It is possible, indeed, that they are masses of young stages in the development of spermatozoa, which have become free in this somite, or a portion of the sperm-sac, which after rupture of the septa might come to lie here, or again cysts of Monocystis. As to the organs which he described as "testicules" in somite xii., there is little doubt but that he was dealing with the sperm-sacs, for he found "spermatiques filaments" attached to central |
