SUMNER: KUPFFER'S VESICLE 63 



to the neurenteric canal, while KUPFFER held it to be anterior to the latter. The 

 real representative of the " Raphe" or line of union of the blastoderm edges of the 

 shark, KUPFFER found in the so-called " Caudal Knob" (Randhugel) appearing at 

 an early period .at the posterior end of the trout embryo. This comparison was 

 based upon the supposition that the " prostoma," or blastopore of the meroblastic 

 vertebrates, was originally situated upon the blastoderm margin as in the shark, and 

 that its more anterior position in Teleosts and Amniota had been due to a removal 

 from its primitive situation. It is not plain, however, whether or not KUPFFER 

 regarded this change of position as occurring in the ontogeny of the teleosts. 



This original invagination, occurring immediately in front of the caudal knob, 

 resulted in the formation of the much discussed vesicle, which represented that part 

 of the archenteron forming the allantois of the amniota. 



There seems to be no doubt now that the " primitive FIGURE 24. 

 groove " seen by KUPFFER in the trout was nothing more than 

 the medullary furrow. KUPFFER apparently made little use of 

 sections and he does not give a single figure of one illustrating jfcj 

 this point. But his main ideas, namely, that there occurs in 

 the teleosts a dorsal invagination comparable to that in the rep- 

 tile, and that this invagination has been removed from a prim- '-^^..^f^ ^" ~7 



itive marginal position, are fully borne out by the present in- 

 vestigations. I differ from KUPFFER, however, in regarding the Not s embryo after ap- 

 pearance of caudal knob 

 "prostoma" as representing only a limited part of the blasto- (<*). 



pore, the remainder being constituted by the entire blastoderm 

 margin (KUPFFER'S " Blastotrema"). Again I find strong evidence that this detach- 

 ment of the "prostoma" from the margin occurs in ontogeny in the teleost as well 

 as in the elasmobranch, a point left uncertain by KUPFFER. 



If such a process occurs, it must on theory take place some time before the ap- 

 pearance of Kupffer's Vesicle, since this represents the expanded inner end of the 

 " prostoma." Figure 22 shows the condition of a Notunw blastoderm at this period. 

 The indentation of the blastoderm margin and its relation to the future axis of the 

 embryo recall at once the figures, given us by Duval ('84) of the early chick blasto- 

 derm. These will be referred to "later. Figure 23 represents a somewhat more ad- 

 vanced stage and demands no further explanation. Figure 24 shows the appear- 

 ance of an embryo in which Kupffer's Vesicle has formed. The indented posterior 

 margin has now given place to a rounded projection, a condition which we should 

 expect to exist after the final union of the sides of the indentation, in other words, 

 after the detachment of the prostoma from the yolk blastopore. 



