SUMNER: KUPFFER'S VESICLE 



55 



FIGURE 12. 



which showed an open invagination in place of the solid ingrowth. The hypo- 

 thetical primitive condition was shown, with diagrammatic distinctness, in the egg 

 of an unknown eel (Mttraenaf), which it was my good fortune to secure, while at 

 Naples, during the summer of 1899. 1 



Here, as in the preceding forms, the process is 

 initiated by a thickening and indentation of the 

 superficial layer on the embryonic side of the blast- 

 oderm margin (figure 13). The next ensuing stage 

 is represented in figure 14, which demands little ex- 

 planation. Figure 13 represents the condition 

 when the blastopore is still large, while in the next 

 stage only a slender yolk-plug remains. The Vesicle 

 of Kupffer has meanwhile attained a considerable 

 size, so that it is readily visible in the living egg. 

 In the latter there is also to be seen a fine canal con- 

 necting the vesicle with the exterior, through the blastopore, and passing just in front 

 of the yolk-plug. This condition is quite enduring, lasting for perhaps an hour after 

 the appearance of the vesicle to view in the living eggi Sagittal sections removed 

 any possible doubt as to the meaning of -this appearance. Here, as in the forms 



FIGURE 13. 



Posterior eiid of very early Amiurus em- 

 bryo (cam. lac.) showing interesting rela- 

 tion between superficial layer of the epiblast 

 aud the vesicle. 



Sagittal section through blastopore region of early Murxnaf embryo (cam. Inc.). 



previously discussed, there is a direct continuity between the invaginated cell-layer 

 and the lowermost layer of the embryo. 



Previous Observations of a Similar Nature. It is interesting to note that 

 this manner of formation of Kupffer's Vesicle through an invagination from above 

 is identical with that described by KUPFFER himself in 1879. The latter author 

 came to this conclusion from the study of the living eggs of Osmems (see figure 15) 



1 In a paper read before the last session of the American Morphological Society ( New Haven, December 27, 

 1899), I described this case, and referred to the egg as being that of Murasna. I have later learned from Dr. LoBianco 

 that he is uncertain of the genus. 



