THE DEVELOrMENT OF PALUDINA VlVirARA. 113 



mantle cavity to the riglit of the I'ight horn is first noticeable 

 in this stage, but will be more fully noticed in the next. 

 The kidneys have been formed as outpushings of the 

 (morphological) ventral wall of the pericardium on either 

 side; the wall of the little left kidney and the adjoining wall 

 of the left horn of the mantle cavity are cut through in the 

 ventral part of the section in fig. 12 {I. h.), while the right 

 horn is seen more dorsally at r. m. c. The ventral position of 

 the left horn is also seen in fig. D at I. m. c.^ The right 

 division of the pericardium has become much enlarged, and 

 now occupies a very considerable portion of the visceral hump, 

 while the left division remains small, and lies in the narrow 

 region between the liver and the left horn of the mantle 

 cavity. The rectum bends sharply downwards from the 

 stomach and then runs forward ventrally on the right 

 to the anus, which lies just anteriorly to the junction of the 

 two horns of the mantle cavity, and is now included in the 

 latter. 



Stage E (figs. E, E^, E. ; figs. 13 and 14).— The foot 

 has grown back into its definitive position, and is separated 

 by a marked constriction from the head. The features of 

 the visceral hump noticed in the last stage are now accentu- 

 ated. The bulge on the left side has become much more 

 prominent, and is a very characteristic feature, giving, even 

 more than before, the appearance of sinistral coiling when 

 looked at from above (fig. E^). A comparison between figs. 

 12 and 13 shows that the essential relations are the same as 

 in the last stage. The liver, now ventral to the stomach, has 

 increased much in size; the pericardium, of which only a 

 portion of the right-hand division is shown in the figures, has 

 swollen, and is found extending for a considerable distance be- 

 side the stomach to the right of the original right kidney (see 

 fig. El and fig. 15) ; while close to the kidney on the right is 

 found the first rudiment of the heart as a little solid ingrowth 

 of mesoderm cells pushing the pericardial wall before it. 



' Eor further description of tlie kidneys and their rcihition to the mantle 

 cavity, see Part I of this paper. 



VOL. 46, PAKT 1. — NEW SERIES. H 



