98 CHARLES BROOKOVER 



perpendicularly to the surface of the cells so as to make them 

 appear as if there were a second set of shorter cilia. The contents 

 of the cells are granular with large nuclei located slightly deeper 

 than the center of the cell. Frequently there appear to be two 

 or three nucleoli. There are vacuoles in the cytoplasm in certain 

 preparations, but not enough work has been done on the finer 

 structure of the cells to determine whether fat or other substances 

 have been dissolved in the treatment with alcohol or not. In 

 preparations stained with intra-vitam methylen blue or by the 

 Nissl method, there appeared certain cells occasionally, that 

 were a deeper blue than the majority of the columnar cells. They 

 were brought out in some of the iron hematoxylin preparations 

 in which they seemed not quite so granular as the other epithe- 

 lial cells. They are closely applied to the basement membrane 

 from which they taper to a narrow end at the free surface. When 

 the epithelium is viewed from its deeper surface, these cells show 

 radiating arms that seem almost to set them in connection with 

 one another. Thus they look very much as if they form a nerve 

 plexus. These cells call to mind the supporting cells which John- 

 ston ('01) described among the ciliated epithelial cells of the 

 saccus vasculosus in Acipenser. 



Our knowledge of the structure and function of the diverticula 

 of the neural tube of vertebrates is not very extensive. Meek 

 ('07) has studied the choroid plexus of the lateral ventricles of 

 some mammals and has shown that there is a single layer of cubical 

 cells in theepithellium. These are ciliated in the young but devoid 

 of cilia in the adult. He found motile cilia in the adult on the 

 ependymal walls of the ventricles. He shows that nerves are 

 present in close proximity to the blood vessels and that the epithe- 

 lium sometimes has intra-cellular fat globules. There is some- 

 times a cuticular border on the free surface of the epithelial cells 

 of the choroid plexus that, as in Amia, gives them the appearance 

 of being ciliated. Johnston found nerve fibers in the basement 

 membrane of the ciliated epithelium of the saccus vasculosus in 

 Acipenser and, as we have seen that cilia are present and cause 

 motion in the encephalic fluid in Amia where there are nerve fibers 

 in the basement membrane, we might infer that cilia are con- 



