130 B. F. KINGSBURY 



different vertebrates. It is we who draw sharp boundaries, not 

 nature. 



It doubtless will be objected that the notochord originally ex- 

 tends farther cephalad than the point which the present inter- 

 pretation demands, possibly as His thought to the level of the 

 (his) basilar fold. His ('92, 1), in fact, criticised Ahlborn's divi- 

 sion of the brain into epichordal and prechordal parts on the 

 ground that the extent of the notochord in the adult is second- 

 ary and varies from stage to stage and in different forms. 

 This objection is of course valid; notochord and neural tube 

 grow markedly after they are first laid down and at different 

 rates, but it applies equally to His' own interpretation. Such 

 figures as his own ('92, 2) figure 4, of the torpedo embryo, as 

 well as such carefully constructed figures as those of Scammon 

 ('12) for Acanthias, among others, indicate that the notochord 

 in early stages, when first formed, does not extend forward to the 

 basilar fold as the His interpretation demands. 



It is evident, however, that our knowledge of the morphologi- 

 cal relations at the anterior end of the notochord is quite inade- 

 quate, and any consideration would involve the interpretation 

 not only of the notochord and neural plate, but as well the pro- 

 tochordal or prechordal plate, so-called preoral entoderm (ce- 

 phalic entoderm), etc.; in fact, all aspects of that intensely in- 

 teresting portion of the head in the immediate neighborhood of 

 the hypophysis. The present interpretation has the merit of rec- 

 ognizing the distinction of epichordal and prechordal portions 

 of the brain tube as primary and not secondary, and of offering 

 an explanation of the significance of this distinction. ^ 



^ In terminating this paper the writer wishes to acknowledge the helpful 

 jeditorial comments of Prof. C. J. Herrick. 



