68 Journal of Comparative Neurology. 



the origin of the superficial layer is described. "This remark- 

 able assemblage of superficial cells with dividing nuclei, karyo- 

 kinetic figures and other evidences of proliferation may be read- 

 ily seen in the cerebellum of old embryos of the guinea-pig. 



We observe that in an older embryo a much larger por- 

 tion of the dorsal surface has been thus covered, and evidently 

 from behind forward. A transverse section of the cerebellum 

 near its base in a mouse embryo of a little older stage, shows 

 that the entire surface has now been covered by the prolifer- 

 ating zone, but that it is curiously double, with a layer of white 

 fibres separating the two zones. It is also observed that the 

 walls of the nerve tube at the recessus lateralis of the fourth 

 ventricle are very thin, and consist of rapidly proliferating and 

 hence closely-packed cells which pass from the ental to the 

 ectal surface. This section suggests that possibly the lateral 

 and caudal portions of the ventricular surface of the cerebellum 

 may be the sources of the proliferating superficial layer of the 

 dorson." The form of this statement m.ay have led Schaper 

 to speak of our statements as '* Vermuthungen " but the arti- 

 cle goes on to afford proof that this " suggestion is valid " by 

 a study of the origin of the recessus lateralis. On p. 12 we 

 have "From either side there extends a curious upward fold 

 containing a cavity. The source of the growth is evidently the 

 walls of the cavity as witness the numerous cells clustred at that 

 point." " It will be noticed also that the entire dorsal portion 

 of the organ is affected by this overlapping growth from behind 

 and the sides, so that a groove is formed on either side of the 

 meson, dorsally. " "Fig. 7 well exhibits the extent to which 

 the gray matter of the dorso-lateral aspect of the medulla is 

 derived from the epithelium of the recessus lateralis." One 

 word also respecting the idea that the cerebellum is peculiar in 

 the possession of a transitory superficial proliferating zone. 

 Fig. 4 of Plate II of Vol. I of this Journal was drawn to call 

 attention to the development of a proliferating zone in the cere- 

 brum. Though this zone is not strictly superficial it neverthe- 

 less corresponds to the layer in question and is a centre of mi- 



