30 



CONARIO-HYPOPHYSIAL TRACT. 



the parts of the homologue of the myelencephalon (" cerebro- 

 spinal tract" or abdominal nerve-cord) become wholly on the 

 neural aspect of the body, as in Vertebrates. In both divi- 

 sions the infolding of the side walls completing the central 

 canal occurs on the neural side. In both the nerves arise from 

 the neural summits of such infoldings ; and in both the " ex- 

 ternal skin " would pass from the neural side of the groove 

 into the central (then becoming) ciliate canal. In both the 

 haemal side of the cord would manifest an excess of the "white 

 matter ;" and this with the opposite predominant grey matter 

 would present not " very nearly/' but the very same relative 

 positions to the body of the animal containing them (compare 

 figs. 2 and 3). 



Of these propositions, the base or support is the homology 

 of the pineal, third ventricular, infundibular, pituitary residuary 

 modifications in the Vertebrate brain with the persistent func- 

 tional canal traversing the homologous tract in the x\nnulate 

 or Articulate brain*. 



As animals descend in the scale, the instinctive or reflex 

 actions of the nervous system predominate over those that are 

 " willed," or the voluntary actions. 



* I have elsewhere (' Archetype of the Vertebrate Skeleton,' 8vo, 1848, 

 p. 2) pleaded in favour of single substantive " terms " in place of " de- 

 scriptive phrases," and may here cite, as synonyms of "myelencephalon" — 

 "nervous system" (p. 165), " cerebro-spinal nervous system" (p. 99), 

 " central nervous system " (p. 100), " nervous part of the brain and spinal 

 cord " (p. 100) ; again, as synonyms of " myelon " — " spinal marrow," 

 " spinal cord," " abdominal nerve-cord " (p. 165), " Annelid nervous 

 cord " (ib.) ; also, as synonyms of " myelonal canal '' — " medullary canal " 

 (p. 128), " neural canal " (p. 100), " central canal of the nervous system," 

 equivalent to " myelencephalous canal " spinal canal " (p. 99), which, 

 in surgery, is a synonym of " vertebral canal." The pages here quoted 

 refer to the ' Elasmobranch Fishes ' of Balfour, 



