376 



GILMAN A. DREW. 



become permanently settled near the ganglia at points nearly- 

 opposite their points of origin. As the same relation between 

 organs in this region is retained during the whole of the 

 development^ there is no reason to think that growth is more 

 from one side than from another. If, then, the otocystic 

 canals are remnants of the original invaginations, we might 

 expect them to run almost perpendicular to the surface 

 instead of opening so far anterior and dorsal. It might be 

 thought that the development of the anterior foot muscles 

 has crowded the stomach, ganglia, and otocysts posteriorly. 



3tc> 



Text-fig. W. — Horizontal section of the foot of an adult Nucula delpiii- 

 nodonta. Tlie otocystic canals leave the dorsal side of the otocysts, so 

 that in this section only the dorsal wall of the otocyst is seen on the side 

 where the canal is present, afni. Anterior foot muscles, i7it. Intestine. 

 nc. Otocystic canal, ot. Otocyst. jtg. Pedal ganglion, sto. Stomach. 



and caused the otocystic canals to take up this position, but 

 reference to fig. 64 will show that before these muscles 

 become very large the otocystic canals open further toward 

 the anterior than when these muscles become highly deve- 

 loped (Text-fig. W). This seems to show that the muscles, as 

 they develop, project anteriorly, and do not affect the organs 

 lying behind them. 



In a former publication (1) I have described the imperfect 



