844 PEOF. G. C. BOURNE OX THE [ISToV. 17, 



traced to its aperture, which in Septaria lies some way in front of 

 the anal and ovipository apertures, the epithelium of the duct 

 is seen to pass without any distinction of histological character 

 into the epithelium of the adjacent part of the mantle-cavity, 

 which latter is not in this place glandular, as it is close by the 

 anal and uterine orifices, but is a simple ciliated columnar 

 epithelium resembling the epithelium of the terminal portion of 

 the vaginal duct in the minutest particulars. Tlie ductus enig- 

 maticvTS opens into a region of the mantle in which the epithelium 

 has been greatly moditied by the abundant development of long 

 beaker-shaped mucous cells, and in this case the transition from 

 the epithelium of the duct to that of the mantle is abrupt (fig. 6)., 

 From a consideration of these facts I am inclined to the opinion 

 that the whole of the sperm-sac and its two ducts is also formed 

 as an invagination of the mantle-epithelium, and that therefore 

 the whole of the accessory organs contained in the genital complex,, 

 with the exception of a short length of the oviduct, are ectodermal 

 structures secondarily attached to the oviduct ; and in this I differ 

 from Thiele (39), who regards the whole of the vagina and sperm- 

 sac (which he calls the receptaculum seminis) as the rej)resentative 

 of the right kidney of the Neritidie. There can be no doubt that 

 the distal portion of the oviduct repi^esents a part, probably the 

 terminal part or duct, of the right kidney. The existence of the 

 oviduco-coelomic funnel is sufiicient evidence of this homology.. 

 But in my opinion the limit between kidney derivative and 

 ectodennal derivative is indicated in Septaria )3y the opening of' 

 the oviduct into the thalamus. Hei-e tiiere is an abrupt change 

 in the histological character of the ej^ithelium, and a reference to 

 figs. 3, 13, & 16 shows that the thalamus and the egg-duct 

 intervene between the oviduct and the sperm-sac. I have given 

 strong reasons for believing that all the glands of the thalamus and 

 egg-duct are derived from the ectodei-m : and if I a-m right this 

 circumstance militates against Thiele's view that the spermato- 

 phore-sac represents the right kidney, for it can hardly be- 

 maintained that ectodermal structures have pushed their way into- 

 the primitive kidney and divided it into two widely separated 

 parts, one opening to the exterior, the other communicating with- 

 the ccelom by a ciliated funnel. 



I am unable to give a description of the male organs of Sejjtaria, 

 as all the specimens that I have examined by means of sections, 

 were females. 



From an inspection of fig. 4 it might be inferred that the 

 extensive tubular gland lying in the dorsal bodj^-wall to the right 

 of the rectum, and therefore occupying on the right side of the 

 body a position similar to that occupied by the kidney on the left,, 

 is a representative of the glandular part of the right kidney. 

 Such an inference, however, cannot be sustained. The histological 

 chai-acters of the gland in question are indistinguishable from 

 those of the hypobrauchial mucous gland of other Rhipidogloss 

 (e. g. Fissurella). Tlie anterior lobe of the gland lies immediatsly 



