116 ISABELLA M. PRUMMOND. 



on either side of the oesophagus to about the region where 

 the anus opens, when they appear to lose themselves in the 

 epithelium of the floor of the mantle cavity. The morpho- 

 logically left connective is by far the stronger, and arises 

 behind, just below the anus, while the morphologically right 

 appears at the extremity of the right extension of the 

 mantle cavity. The two connectives are thus separated by a 

 considerable distance posteriorly, and they are not at present 

 united by a commissure. 



Stage G (fig. G and fig. 16). — The original apex of the 

 visceral hump now points ventrally, though it is still more 

 prominent on the left side than on the right, which gives the 

 appearance, when the animal is looked at from above, of the 

 visceral hump being set crookedly upon the foot. The 

 oesophagus is elongated, and bends sharply downwards to 

 open into the stomach. The stomach itself is much enlarged 

 and lies chiefly ventrally, but ascends somewhat to open into 

 the rectum, which then bends dorsalwards and runs forward 

 in the roof of the mantle cavity' to the anus. The mantle 

 cavity now extends far down on the left side, especially 

 posteriorly, and a portion of the kidney is visible in a view 

 of the left side of the animal. The rudiments of the 

 ctenidium are clearly formed as projections from the roof of 

 the mantle cavity on the left. The kidney duct soon after 

 leaving the kidney now passes below the rectum and runs 

 backward on its right side to open into a sort of little pouch 

 of the mantle cavity together with the genital duct, as the 

 original left kidney duct may now be called. Von Erlanger's 

 fig. 2, pi. xsii, shows very well the disposition of the kidney 

 duct at this stage. The old relations of the rectum to the 

 two original horns of the mantle cavity are thus disturbed, 

 apparently by a drawing together of the edges of the mantle 

 cavity in this region, the space between the two ducts being 

 obliterated. The whole, or very nearly the wliole, of the 

 definitive mantle cavity seems, therefore, to be formed by 

 the great extension of the original right horn, as noticed in 

 Stage ¥j. In other respects the mutual relations of peri- 



