492 Prof. A. Dendy. On a Pair of Ciliated Grooves 



acting in conjunction with the longer cilia which line other parts of 

 the brain-cavity. The occurrence of cilia in some part or other of the 

 central nervous system of vertebrates has been so often demonstrated'"" 

 that it is hardly necessary to discuss other cases here, except to point 

 out that their function is probably in all cases to promote the circula- 

 tion of the brain-fluid. 



As to the choroid plexuses of the vertebrate brain there can, I 

 venture to think, be little doubt as to their importance in promoting 

 the oxygenation of the brain-fluid. Especially suggestive from this- 

 point of view is the manner in which these plexuses sometimes project 

 into the cavities of the ventricles. A good example of this is afforded 

 by the vertical septum of the choroid plexus of the mid-brain in the 

 New Zealand Ammoccete, as described above. This septum is highly 

 vascular, and it is extremely significant that the ciliated grooves ate 

 so arranged as probably to direct a stream of brain-fluid along each 

 side of it. Whether the direction of this stream is forwards or back- 

 wards, it is of course impossible to say without direct experiment. 

 Personally, I am inclined to think that it will be found to flow forwards, 

 and that the ciliated grooves may be looked upon as special organs for 

 conveying an abundant supply of oxygenated fluid to the forepart of 

 the brain (especially, perhaps, to the right ganglion habenulae, which, 

 as is well known, is enormously developed in the Lamprey, and 

 apparently fulfils some important function in connection with the 

 parietal organs). In the young Ammoccete the first choroid plexus, 

 which may be supposed to be especially concerned in the respiration 

 of the fore-brain, is not yet developed ; the second and third choroid 

 plexuses, belonging respectively to the mid- and hind-brain, are, on the 

 other hand, already extensive. We need not, therefore, be surprised 

 to find that the fore-brain at this stage is dependent to a large extent 

 for its means of respiration, and perhaps also for its nutrition, upon the 

 choroid plexus of the mid-brain, and that a special apparatus is 

 developed for securing a forward flow of the necessary fluid in the 

 brain-cavity. With regard to this fluid itself it is interesting to note 

 in this connection the recently expressed opinion of Minot :f " The 

 pineal region develops a series of structures, which, from their 

 anatomical characteristics, appear to be directly concerned in the 

 formation of the fluid in the cavities of the brain. We may assume 

 that the choroid plexus supplies the main bulk of the fluid, but the 

 gland-like organisation of the epiphysis and of the paraphysis indicates 

 that they supply by secretion special chemical substances to the 

 encephalic fluid." 



* See for example Klein, 'Quart. Journ. Micros. Sci.,' vol. 20, N.S., p. 476 ; 

 Eetzius, ' Biologische Untersuchungen,' Neue Folge, vol. 6, p. 59; Beard, 

 ' Aiiatomischer Anzeiger,' vol. 3, p. 902. 



t ' American Journal of Anatomy,' vol. 1 , No. 1, p. 96. 



