12 rUOCEEUr.NGS OF THE 



striking evidence of the way in wliich these euriy fishes may Lave 

 arisen from their conti^inporary Palajostracan rivals. It must 

 always he reineinberccl that these latter animals were not Crusta- 

 ceans or Arachnids, but tlie precursors ot" both of these groups, 

 and much nearer to their origin from the Annelids than the 

 ])resent day Arthropoda. To this circumstance must be attributed 

 the annelid characteristics so markedly found in the Vertebrate, 

 especially in the excretory organs. 



It seems lo me highly probable that this same law of upward 

 progress, viz., that each successive group has arisen from some 

 member of tlie highest group existing at the time, holds good 

 also for the vegetable kingdom, especially in view of the statement 

 recently made that Phanerogams arose from Cycads, I hope that 

 the President may see his way to offer a few remarks on that 

 aspect of the question. 



The great stumbling block lo the acceptance of my theory ia 

 the minds of many, ia the necessity of making a new digestive 

 tube in a highly organised animal, aud yet the same zoologists 

 accept without the slightest dilliculty, as a commonplace, the 

 manufacture of a new respiratory organ for breathing air instead 

 of water in the transition from the fish to the amphibian. The 

 previous factor in that case was the swim-bladder which provided 

 the new organ, in tlie other a respiratory chamber formed by the 

 internal gills ; for one of the great characteristics of many members 

 of the Palaeostracan group is the absence of external gills and 

 the indication of internally situated gills, and it does seem to me 

 that the evidence is stronger in favour of the Vertebrate alimentary 

 canal being formed from a {)reexisiing respiratory chamber, than 

 that an alimentary canal should have taken on a respiratory 

 function in its anterior end. 



The way in which the alimentary canal is innervated by the 

 downgrowth of the great respiratory nerve, the vagus, which is so 

 clearly a segmental nerve for the respiratory part but not for the 

 small intestine, points to this conclusion. The fact that in the 

 Avell-marked segmental respiratory chamber of Ammocoetes a new 

 unseginented alimentary tube should be formed at transformation, 

 again indicates that a segmented respiratory chamber was the pre- 

 cursor of an alimentary canal. Finally, the position of the anus 

 in such a form as Drepanaspis and Bothriolej)is immediately 

 following upon the region of the head-shield, suggests strongly 

 that in these most ancient and extraordinarily formed fishes the 

 anus followed close upon the mesosoraatic or respiratory region 

 just as it does in such an animal as Limulus. 



Finally in this sketch, not of details but of general principles, 

 I come to the argument that this theory is untenable because it 

 contravenes the fundamental principles of ontogeny. 



Against tliis slatement I most strongly protest, for the strength, 

 I might almost say the main strength, of my position is based on 

 the facts of Vertebrate development. 



The one great principle of ontogeny is the L.iwof Recapitulation, 



