552 BIOLOGICAL PHYSICS 



elements and the consequent shrinkage of the intra- 

 cerebro-vesicular cavities and the medullary canal, 

 gradually appear the ciliary projections on their lining 

 epithelium, as well as on that of the evolving coccygeal 

 gland and of the pituitary body on both ends of its 

 developing elements, i.e. both from within the infundi- 

 bulum on the one end and the buccal cavity on the other. 



What does all this mean ? Simply, what the appear- 

 ance of a ciliary lining membrane always means, that it 

 has been developed or evolved for the purpose of aiding 

 and maintaining circulation along open passages or con- 

 stricted lumina, where gravitation, capillary attraction, 

 and other physical agencies require such assistance. We 

 must, therefore, recognise in this very early appearance 

 of this circulatory adjunct, that the principle of circulation, 

 wherever it has appeared, is the greatest function sub- 

 served by the cavities, or passages, involved, and that, 

 if it were necessary to use this fact as a histological 

 evidence of the claim, which we elsewhere advanced, for 

 the truth of cerebro-spinal lymph circulation and excretion,, 

 we are absolutely entitled to it for such a purpose, for, no 

 doubt, were we meeting it " for the first time " in any 

 hitherto unknown line of research, we would be warranted, 

 nay, compelled, to give a reason for its existence. 



Moreover, the occurrence of a pre-natal ciliary epithelium 

 on the lining membrane of the naso-pharynx, and the 

 glosso-cesophageal mucosa, speak of a continued passage 

 of material from the central brain spaces through the 

 intervening uniting structural media, established for the 

 great functional purpose of conveying into the stomach, 

 when deglutition was both structurally and functionally 

 impossible, the residual products of brain waste to become 

 part of the meconial mass occupying the alimentary canal, 

 when as yet no substance of an alimentary character had 

 been admitted thereto. At this stage of foetal existence, 

 the greater part, or, it may be, the whole of the circu- 

 latory work between the cavities of the skull, the mouth, 

 the lungs, and the alimentary canal, is due to the action of 

 the ciliary epithelium and underlying mucosa of their 

 lining textures. 



Post-natally, an alteration takes place in the lining 



