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, sj). sac). 



[In P. heteroporiis, 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 (geji. 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. heteropoTus 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 uncer- 

 tain 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 

 taches germinatives," but adds his doubt on the matter of interpre- 

 tation 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 



