9n 



And now, what of the last condition? This also is satisfactorily 

 met. In all cases the oral hypophysis has a special, and indeed large, 

 process of nervous matter, the processus infundibuli or neural hypo- 

 physis; which is derived from the posterior part of the fore brain, 

 from the base of the infundibulum. This process is concerned with 

 the innervation of the oral hypophysis alone. Only in Myxine and 

 Petromyzon, so far as my researches extend, (possibly also in 

 Protopterus) this nervous system is not rudimentary. In most 

 Vertebrates the neural hypophysis, which, as KöLmcEii aptly remarks, 

 is at first composed of the same cell elements and fibres as the rest 

 of the brain, degenerates, and in very many full grown animals forms 

 a mass of tissue whose structure many observers have compared to 

 that of the suprarenal bodies which are also masses degenerated tissue. 



The neural hypophysis is thus the most remarkable structure 

 in the whole of the vertebrate central nervous system. Though de- 

 generated, it still clings to the traditions of its ancestry, for even, as 

 it were, in its death it is closely and almost inseparably connected 

 with the rest of the hypophysis, especially in Mammalia and in Dipnoi. 



In Myxine alone of all Vertebrates the old mouth still retains 

 some of its functions as a mouth : it conducts the water of respiration 

 to the gills. In this case, even, changes have occurred, for the nose ^ ) 

 has also got partly into the passage of the old mouth. If it be true 

 that the nose was once a branchial sense organ — which view, in spite 

 of Gegenbaur, I still maintain — then, for purely physiological con- 

 siderations its taking a position in the passage of the old mouth 

 in Myxine is very obvious. 



It is a well known fact that what I call the old mouth in Myxine 

 is purely respiratory, conducting water into the gills, and what then 

 could be more likely than that one of the branchial sense organs 

 should be, as it were, told off to do duty at its entrance. It is cer- 

 tain, from Goette's and Dohrn's observations, that these passages in 

 Myxine and Petromyzon are the representatives of the oral hypo- 

 physis, and all I claim here is the identification of the hypo- 

 blastic opening in Myxine as the (modified) opening of the old 

 mouth into the gut. I have gone over and extended these obser- 

 vations and can fully confirm Dohrn in nearly every point. 



If the above morphological comparison can be maintained, and 



1) In Petromyzon Dohen finds that the nose is at first a special 

 depression apart from the hypophysis invagination. The latter lies between 

 nose and mouth. 



