HYPOPHYSIS. 287 



the hypophysis to the front end of the notochord are as con- 

 stant as its relations to the infundibulum. So close is the 

 apparent relation of the hypophysis to the notochord that 

 at least one zoologist, HUBRECHT, has suggested that there 

 was originally a functional connexion between the two 

 structures. 



Again, in the embryo of Acipenser, the sturgeon, as 

 shown by KUPFFER, the distal end of the hypophysis 

 undergoes temporary fusion with the subjacent wall of 

 the alimentary cavity. In spite of the extremely modified 

 character of the embryo of Acipenser (the embryo being 

 flattened out like a disc over the yolk), Kupffer regards 

 this fusion of the hypophysis with the endoderm as being 

 of great morphological significance. 



On the contrary, for the reasons mentioned above, I 

 would regard all these fusions of the hypophysis in the 

 craniate Vertebrates, whether with the infundibulum, 

 notochord, or endoderm, as being of an entirely incidental 

 character, often due, perhaps, to a tendency of such con- 

 tiguous embryonic tissues to fuse together. 



I therefore suggest that : The liypopJiysis arose in con- 

 nexion zvit/i a functional neuropore ; wJien the neuropore 

 ceased to be functional, tliere ^vas no longer any bond of 

 union between its inner portion, whicJi opened into the 

 cerebral cavity, and its outer portion, wJiich opened into the 

 buccal cavity ; and these two portions became separated by 

 differential growth of the cerebral and body-walls (cf. Fig. 

 135). 



The Ascidian Hypophysis. 



The development of the hypophysis in a typical As- 

 cidian, its constriction from the wall of the cerebral 

 vesicle in the form of a tube, and its opening into the 



