76 MEMOIRS OF THE NEW YORK ACADEMY OF SCIENCES 



I am convinced, from the mode of formation of Kupffer's Vesicle, that it has no 

 morphological relation to these lower cavities in the periblast. In such cases as 

 those of Ctenolabrm the connection is doubtless a secondary one. But there prob- 

 ably exists, as I maintain below, a physiological connection between the two. 



VIII. THE FUNCTION OF KUPFFER'S VESICLE. 



The .preceding pages have been largely concerned with a morphological interpre- 

 tation of the embryonic structure known as Kupffer's Vesicle. It is obvious that 

 this morphological interpretation in no way accounts for the dimensions attained by 

 the vesicle during development. Why should the lumen of this quite transitory 

 post-anal-gut reach such a relatively enormous size at a time when, in the remainder 

 of the gut, no lumen has appeared? Kupffer's Vesicle must be regarded as an em- 

 bryonic organ having some definite part to play in the economy of the growing em- 

 bryo. The measurements made by Henneguy located the region of growth in the 

 unsegmentated part of the embryo lying between Kupffer's Vesicle and the last 

 formed somite. Here, then, metabolism is most active, and the material needed for 

 growth ought to be the most abundant. It is now a generally accepted fact that the 

 periblast with its giant nuclei play a leading role in the assimilation of the yolk. 

 Passing upward from the deeper layers of the yolk, we find that the yolk spheres 

 become successively smaller, while in the periblast syncytium they are reduced to 

 minute granules. Finally, there seems to occur a thin fluid layer between the peri- 

 blast and the cells of the embryo proper. I have already noted the occurrence of a 

 large vesicle in the yolk beneath the growing region of the embryo in certain fishes. 

 Around this vesicle the periblast and its contained nuclei are especially abundant, 

 and within its interior there is to be seen in sections a fine coagulum, reticulate in 

 appearance, which seems to be of an albuminous nature. It has for some time been 

 my view (SUMNER, '99, a), that this vesicle contains a more fluid yolk, partially 

 assimilated through the activity of the periblast, and intended for the nourishment 

 of the growing embryo. I have, also expressed the view ('99, b) that Kupffer's 

 Vesicle itself represents an embryonic digestive organ (more properly an organ of 

 absorption). Its relation to the yolk vesicle has already been dwelt upon. Within 

 it, moreover, occurs a coagulum which is similar to that found in the other. 

 SOBOTTA ('98) has commented upon the fact that Kupffer's Vesicle contains a fluid 

 having a refractive index higher than that of water. I find in the case of Scorpsena, 

 that this is noticeably true at an advanced stage in the development of the vesicle, 



