l6o CONK LIN. [Vol. XIII. 



remain about the same size as before, Figs. 93, 95, 98. The 

 nuclei of the entoderm cells stain deeply, and they are not 

 round, but angular and irregular, as if they had been pressed 

 out of shape by the yolk spheres which closely surround them. 

 In Figs. 102-104 the entoderm cells at the inner end of the 

 stomodaeum extend around the yolk on the right anterior side 

 nearly to the intestinal cells, while the left and lower part of 

 the yolk is still composed of the large pyramidal yolk cells. 



At first the cavity of the stomach is straight. It lies in 

 the median plane of the embryo, and throughout its whole 

 course preserves an antero-posterior direction. When the shell 

 gland and the foot attain to considerable size, the whole pos- 

 terior part of the embryo is pushed toward the ventral side, and 

 the course of the stomach, while still in the median plane, no 

 longer lies in the line connecting the most anterior and pos- 

 terior points of the embryo ; its anterior end lies slightly above 

 this line, while its posterior end is much below it, Fig. 92. 

 In more advanced stages the posterior end of the embryo is 

 pushed still farther toward the ventral side, and at the same 

 time is twisted around anteriorly and to the right. The pos- 

 terior part of the stomach is now bent downward at an angle 

 of nearly 90° with the anterior part, Fig. 93, and at the same 

 time it is turned anteriorly and to the right, and its point of 

 junction with the intestine, i.e., what was primarily its pos- 

 terior end, is carried up on the right side of the embryo, until, 

 as shown in Figs. 80, 81, it lies far up toward the dorsal sur- 

 face. 



Comparisons . 



In its general features the formation of the enteron is essen- 

 tially the same in all gasteropods so far studied. The intestine, 

 or hinder portion of the alimentary canal, is formed of clear, 

 protoplasmic cells, called the " cylinder cells " by Rabl ('79), 

 the " Darmplatte " by Blochmann ('81), while the stomach is 

 bounded by relatively large cells which contain more or less yolk. 



In particular the account of these processes given by 

 Bobretzky ('77) for several prosobranchs is very similar to the 

 account which I have given for Crepidula. However, when one 



