328 



GILMAN A. DREW. 



causes the bend where the intestine joins the stomach to 

 become quite abrupt. 



At the same time that the stomach, moves dorsally, the 

 cerebral ganglia (fig. 34, eg.), which are still a mass of rather 

 undifferentiated cells, are carried up, and come to lie poste- 

 rior and a little ventral to the anterior adductor muscle (aa.). 

 The foot (/.) retains its position beneath the intestine and 



int rl og 



Text-iig. J. — Reconstruction of an embryo of Yoldia limatula at a stage 

 during casting. Represented as seen from the right side, with the right 

 shell-valve and mantle lobe removed, aa. Anterior adductor muscle. 

 cff. cerebral ganglion. /. Foot. ^. Rudiment of gill. ifif. Intestine. 

 ot. Otocyst. pa. Posterior adductor muscle, p^. Pedal ganglion, r. 

 Pouch tliat leads to the cerebral ganglia, rl. Right lobe of the digestive 

 gland. Stomodaeum. Adhering test cells, y^. Visceral ganglion. 



stomach, and in the general dorsal movement is carried a 

 little further from the margin of the shell. A similar stage 

 for Yoldia is represented by Text-fig. J. At the end of several 

 hours the stomodseum (fig. 34, std.) breaks across near the 

 tip of the foot, and together with the apical plate and the 

 remnants of the test cells is thrown away. From appear- 

 ances I am inclined to believe that the whole of the apical 



