396 W. H. GASKELL. 



ventral middle line of the epichordal portion of the brain of all 

 Vertebrates, which is known by the name of the raphe, is due 

 to the breaking down of the two apposed layers of cylindrical 

 epithelial cells which originally lined the central cavity in this 

 position. Doubtless the closeness of the apposition of these 

 cells by which the lumen was obliterated was due very largely 

 at first to the interlacement of the cilia with which these cells 

 are provided, and not simply to commencing degenerative 

 changes. 



With respect to the question whether the lining cells of the 

 cavities of the central nervous system are ciliated or not, the 

 literature of the subject shows that a considerable discrepancy 

 of opinion exists. In a recent paper from Johns Hopkins 

 University, Wightman (8) gives a list of observers for and 

 against the occurrence of cilia in this region, and concludes 

 from his own experiments that cilia are undoubtedly present 

 in the ventricles of the frog. As to Petromyzon, Ahlborn (3, 

 p. 249), speaking of the transition of the central canal of the 

 cord into the cavity of the fourth ventricle, says that " the 

 epithelium of the central canal, where it passes into the epen- 

 dyma of the brain-cavities, undergoes a considerable elonga- 

 tion of its cells ; the cilia are conspicuous to the view, and one 

 can easily recognise a long oval nucleus in the body of the cell, 

 as well as a tailed prolongation which passes deep into the brain 

 substance." Rohon (6) figures isolated cells of P. marinus 

 with cilia attached; and Owsjannikow (7) describes the epithe- 

 lium in the neighbourhood of the optic thalami as composed of 

 cells, each of which bears a single cilium. 



My preparations, especially those stained with osmic acid, 

 present appearances as of ragged, irregular projections protrud- 

 ing into the lumen of the cavity ; in some places these appeared 

 to resemble a close-set fringe of cilia, in others they presented 

 single projections or a loose sort of network. Such appearances 

 might be caused by a breaking down of the edge of the cells 

 turned towards the lumen, or they might be due to a ciliated 

 edge, the cilia of which were more or less matted together and 

 cut at dift'ereut angles, as well as mixed up with the shreds of 



