142 Journal of Comparative Neurology. 



brain, nevertheless is proven to derive its peripherally 

 distributed cells (which form its essential elements) from 

 the proliferating cells of the ventricular epithelium.' 



In lower animals, at least, the migrations of cells to 

 reach their definitive station is facilitated by transitory 

 folds which are subsequently obliterated by adhesion. In 

 the same way masses of proliferating cells are apparently 

 transported into the very midst of massive portions of 

 these centres. Neglecting details then, the growing brain 

 is supplied with factories for the production of nerve cells 

 which may continue in operation a longer or shorter time 

 according to circumstances. 



Closely connected with the problem of origin is that 

 of subsequent nutrition of nervous structures. While in 

 some cases the branching protoplasmic process of nerve 

 cells may be traced to the immediate vicinity of blood ves- 

 sels, it is doubtful whether their purpose is the collection 

 of nutriment, while it is certain that some cells must be 

 dependent on other sources of supply. 



It is probable that the lymph which is continually 

 oozing through the pulpy tissue of the brain may have 

 much to do with these processes. Still there is evidence 

 that certain cells • which arise in common with nerve cells 

 and may be transformed into them have a temporary or 

 permanent function of elaborating nervous substance for 

 the active brain cells. Analogies are not wanting for this 

 process. It is suggestive that, in those regions where very 

 sudden and powerful discharge is required, these small cells 

 are extraordinarily numerous. Thus, in the cerebellum, to 

 every functional (Purkinje) cell there are hundreds of the 

 corpuscles which possess almost no protoplasm of their 

 own. 



I. This statement, first made by the writer, has recently received 

 the powerful support of Professor Wilhelm His, of Leipzig. 



