HYPOPHYSIS. 285 



olfactory lobe abuts against the olfactory pit, and, in fact, 

 in young individuals opens into it by the neuropore 



(Fig. 45). 



On the view which I have urged above, that the 

 olfactory pit of Amphioxus is homologous with the 

 hypophysis cerebri of the craniate Vertebrates, it must 

 be assumed that in the latter forms, the neuropore hav- 

 ing ceased to be in any way a functional organ, the hy- 

 pophysis, which has likewise become (morphologically) a 

 vestigial structure, has been mechanically separated from 

 the neuropore, with which it was primitively in functional 

 connexion. It must be supposed that this separation of 

 the hypophysis from the neuropore has been effected by 

 the more rapid downward growth of the ectoderm (from 

 which the hypophysis arises) than of the wall of the brain, 

 so that the hypophysis has been carried farther round to 

 the lower side of the head than the neuropore (Fig. 135). 

 The reason for this unequal growth of the external body- 

 wall and of the cerebral wall may, perhaps, be sought for 

 in the great and independent increase in the cubical con- 

 tents of the brain. 3 



We thus arrive at the conclusion that the present 

 relation of the hypophysis to the infundibulum in the 

 craniates, however intimate it may be in some cases, is, 

 nevertheless, incidental and secondary. 



That this conclusion is not so strained as might appear 

 at first sight is clearly shown by the fact that the in- 

 fundibulum is not the only structure with which the 

 hypophysis enters into close relations. 



In the exceptional cases of Myxine and Bdellostoma, 

 for instance, the distal end of the hypophysis has nothing 

 to do with the infundibulum, but actually opens into the 

 pharynx. In these hag-fishes, as also in the lamprey 



