60 PROCEEDINGS OF THE MA.LACOLOGICAL SOCIETY. 



side by side with the rectum, and opens in the anterior portion of 

 the mantle - cavity immediately above the genital groove (PL VI, 

 Fig. 5, g.g.). 



The female genital organs (H. VI, Fig. 2) are very similar ; the 

 ovary (ov.) gives origin to two fine ducts, which fuse to form the 

 oviduct (ov.d.). On reaching the mantle - cavity, this structure 

 becomes greatly enlarged, its walls take on a glandular character 

 [ov.d'.), and eventually, after running parallel with the rectum for 

 the greater part of its length, it opens into the anterior portion of 

 the mantle-cavity. There is in addition a crescent-shaped accessory 

 oviducal gland (ov.g.), communicating by means of a fine duct with 

 the oviduct. 



The most interesting structure in the anatomy of Turritella is 

 a remarkably well developed groove (IT. VI, Fig. 2, g.g.) running 

 along the floor of the mantle-cavity throughout its entire length ; 

 it is bounded on either side by fleshy ridges consisting of vacuolated 

 tissue (PL VI, Fig. 5, g.g ). 



The groove lies close to the columella muscle (cm.), and at its 

 posterior extremity the two ridges enclosing it become free from; 

 the floor of the mantle-cavity (LI. VI, Fig. 6, g.g.) and abut on the 

 kidney (k.). 



The cells lining the groove and sides of the ridges do not appear 

 to be in any way specialized ; some few of them are ciliated, but 

 this ciliation is by no means a conspicuous feature. The anterior 

 and extra-pallial portion of this structure is slightly modified; the 

 ridge on the right side becomes vertically enlarged, and forms a very 

 conspicuous fold, situated on the right side of the head and under- 

 neath the tentacle (LI. VI, Fig. 1, g.f.). The ridge bounding the 

 left side of the groove becomes much smaller, and finally disappears 

 when it reaches the head of the animal. This groove, with its 

 associated structures equally well developed, is present in both male 

 and female specimens of Turritella. 



In all probability one of its functions is, either to carry away, or 

 receive, the genital products, for the openings of the vas-deferens and 

 oviduct are situated almost immediately above it ; it is, however, only 

 the anterior portion that can be of use in this way, for the genital 

 ducts open in the anterior region of the mantle-cavity quite close to 

 its termination. "What, then, can be the meaning of the extension of 

 the groove to the extreme end of the mantle-cavity ? 



It is so conspicuous a structure that it must have some definite: 

 function. Its posterior end abuts on the kidney (LI. VI, Fig. 6), and: 

 is near the aperture (Ic.o.), placing the excretory organ in communi- 

 cation with the mantle-cavity; it may therefore serve to carry away 

 excretory products. In addition, it might serve to direct a current of 

 water out of the mantle cavity, and so aid in respiration [Clarke, 2] 

 (p. 332) ; any excretory products accumulated in the groove would at 

 the same time be washed away by this stream of water. It seems 

 strange that there should be a comparative scarcity of cilia on the 

 epithelium of this structure, as the efficiency of maintaining a constant 

 current of water down the groove would be greatly increased by the, 



