MUSEUM OF COMPARATIVE ZOOLOGY. 



191 



the larger portion of the ganglion ; they are thicker and shorter thau 

 the cerebro-pedal connectives, from which they are separated by only a 

 narrow space. 



The cerebral comniissnre is much shorter than before (Plate X. 

 Fig. 126), but it has not increased much in thickness (Plate VIII. 

 Fig. 101). lu sagittal sections it is seen to be composed of a central 

 portion made up of nerve fibres cut crosswise and a peripheral layer of 

 nuclei ; but the nuclei are wanting on tlie face of the conmiissure which 

 is in contact with the dorsal wall of the 03sophagus. 



Figure E. — The left surface of a section parallel to the sagittal plane from an embryo of the 



fourteenth day. X 73 



The pedal ganglia (Pkite VIII. Figs. 97-100, Plate IX. Figs. 114, 

 118, 119) lie between the radula sac, which is above, and tlie foot gland 

 whicli is below them. They are nearer together than on the twelfth 

 day, and their anterior ends arc more rounded (Fig. 111). Their pos- 



