MORPHOLOGY OF THE HELIOINID^. 785 



thick-vvalled sac, some little distance in front ot" the hinder end of 

 the latter. This thick- walled sac, which is evidently the repre- 

 sentative of the ootype of the female and of what I have called the 

 terminal chamber in the Neritida?, runs forward in the roof of the 

 mantle-cavity, below and to the right side of the rectum, and 

 opens into the mantle-cavity by a terminal poi-e situated close to 

 the anus. At about one-third of its whole length from the 

 external aperture, the thick-walled sac — which I shall call the 

 terminal sac of the sperm-duct oi-, more shortly, the tei-minal sac 

 — is joined by another sac of considerable diameter. This second 

 sac, which I shall call the diverticulum, opens into tlie terminal 

 sac by a wide apei'tuie, and runs back close to the right side of 

 the latter, to end blindly, sometimes just in front of the entry of 

 the sperm-duct into the terminal sac [A'phanoconia goiddiana, 

 PI. XXXVII. fig. 41) ; in other cases, however, it extends as far 

 back as the hinder end of the terminal sac, and may even project a 

 little beyond it [Alcadia hollandi, fig. 40). The anterior third of 

 the terminal sac, in front of the entry of the diverticulum, exhibits 

 three or four deep transverse constrictions : in section it is round 

 or oval, and the lumen is partly occluded by deep longitudinal folds 

 projecting into it. These folds are covered by a mixed glandular 

 and ciliated epithelium : the ciliated cells of tlu^ familiar kind with 

 attenuated basal ends, the gland-cells tubular with basal nuclei and 

 vacuolated cell-bodies, in Avhich no secretory granules covild be 

 distinguished in well-preserved specimens of Eutrochatella. In its 

 posterior two thirds the terminal sac is laterally compressed so as 

 to be elongate oval in section, and it gives off from each end of the 

 oval and fi'om tlie adrectal side numerous short hollow cjecal out- 

 growths which are sometimes branched, especially in Ajihanoconia 

 (fig. 41). Internally the longitudinal epithelial ridges die out in 

 the posterior two-thirds of the terminal sac, but the epithelial 

 lining both of the cavity of the sac and of the ctecal outgrowths 

 is of very nearly the same character as that of the anterior third. 

 The supporting cells are distinctly ciliated. The epithelium of the 

 diverticulum difiers from that of the terminal sac only in the fact 

 that the gland-cells are full of eosino2:ihilous granules, and the 

 cilia of the supporting cells are longer and rather coarser. The 

 above characters hold good foi' all the species that I have examined, 

 the differences between them being too slight to deserve mention. 

 It may be noted that in Alcadia the hinder moiety of the diverti- 

 culum is constricted a,t very regular intervals (PI. XXXVII. fig. 40). 

 Both in Eittrochaiella and Lucidella I have found in sections a 

 second diverticulum in the form of a slender thin- walled tube 

 opening into a recess of the terminal sac at the same level as, but 

 on the opposite side to, the diverticulum above described. The 

 walls of the recess are lined by a glandular epithelium staining 

 deeply in eosin. The narrow tube runs back in the mantle-wall 

 nearly parallel to the terminal sac and ends blindly just in front 

 of the aperture of the hypobranchial gland. Its hinder end 

 touches and appears to be adherent to the sub-epithelial muscular 



