OF ARTS AND SCIENCES. 71 



seems to be a fundamental agreement in the development of all telo- 

 lecitlial vertebrate ova with respect to the origin of the " chordaento- 

 bl as t," better called invagiuate entoderm, or " invaginate hypoblast" 

 (Scott and Osborn), there is a strong presumption in favor of the 

 opinion that a complete agreement will yet be found to exist in regard 

 to the precise origin of all the cells concerned in the formation of the 

 alimentary tube. It is difRcult to believe that the yolk cells (" Darm- 

 (Mitoblast") form the whole of the mesenteron in Triton, only a part 

 of it in Rana, and none of it in the teleost. Hertwig's observations 

 on Rana have compelled him to admit that the invaginate eutodenn 

 takes a prominent share in forming the mesenteron ; and his figures 

 appear to us not only to warrant this conclusion, but also to suggest 

 even more. Indeed, we think that they lend some support to the 

 opinion that the mesenteron is formed exclusively at the expense of 

 the invaginate entoderm. 



Our observations on the relation of the mesoderm to the entodermic 

 ring are not sufficiently complete to call for separate consideration. 

 So far as they go, they appear to support the view that the mesoderm 

 arises as two lateral masses, separated from each other by chorda cells, 

 and from the periblast by a stratum of cells which, after uniting be- 

 neath the chorda in the manner before stated, are destined to form the 

 mesenteron. 



Kupffer's Vesicle. — Although we have been able to trace the en- 

 tire history of Kupffer's vesicle in several species of ova, its signifi- 

 cance remains as complete a puzzle as ever. Balfour homologizes this 

 vesicle with the terminal dilatation of the " post-anal gut " of the 

 Elasmobranchii, without, however, assigning any grounds for his view. 

 The history of the vesicle is, in many respects, so entirely different 

 from that of the " caudal vesicle " of the elasmobranch embryo, tliat 

 we do not feel ready to accept this interpretation. The interpreta- 

 tions w^iich have been offered by Kupffer and Henneguy are still more 

 unsatisfactory, and need not be considered here. 



Kingslev and Conn were the first to give an accurate account of the 

 origin of this vesicle (1. c, p. 208) ; but they give us no information 

 in regard to its subsequent history, and almost no details of its origin 

 and growth. As they have stated, the vesicle arises by the fusion or 

 confiuence of a cluster of granules ("globules"). These granules are 

 at first few in number (2-4), more or less angular, quite dark, and not 

 more than .002 mm. in diameter. In general appearance, they are 

 not distinguishable from the scattered granules seen in other parts of 

 the ovum. In Cteuolabrus they appear soon after the embryonic ring 



