SUMNER: KUPFFER'S VESICLE 77 



when the outlines of the chorda, seen through the contents of the former, are 

 considerably distorted, this fluid mass serving as a bi-convex lens. 



Microchemical tests as to the contents of the vesicle gave only negative results. 

 I subjected the eggs of. Mtirasnaf and Scorpsena to the reagents employed by LE 

 DANTEC ('90) and Miss GREENWOOD ('94) for the detection of acid in the vacuoles 

 of protozoa. None of these were found applicable to fish eggs, as they either killed 

 the embryo or failed to stain it; but I also used Bismarck Brown. This stain, when 

 neutral, shows a very characteristic reaction in the presence of acids. But no appre- 

 ciable reaction was exhibited by the contents of Kupffer's Vesicle. 



IX. RECAPITULATION. 



1. The hypoblast arises in connection with an invagination of the superficial 

 layer ("Deckschicht") occurring on the posterior border of the blastoderm. This 

 invagination may be an open one (" Munena " possibly some others) or it may be a 

 solid ingrowth of cells (Amiurus, Notwrus, Salvelinus, Fandulus, Ctenolabrus. A 

 similar condition was found in Amia. 



2. This invagination is the " prostoma " of KUPFFER, whose descriptions and 

 theoretical conclusions upon this subject are in the main correct. 



3. Kupffer's Vesicle arises from the expanded inner end of this invagination, 

 when it is an open one ; it is secondarily formed in the invaginated mass of cells, 

 when solid. 



4. Kupffer's Vesicle, as is usually stated, represents the post-anal-gut, the neur- 

 enteric canal being represented by the open duct leading from the vesicle to the 

 exterior in " Murxna " by the solid ingrowth in the other forms named. 



5. A process occurs in the teleosts exactly similar to that folding off of the tail 

 end of the embryo which results in the formation of the neurenteric canal of the 

 elasmobranchs. The main difference between the two cases is that the teleost embryo 

 continues to grow backward at an equal pace with the blastoderm margin, while in 

 the elasmobranch, the embryo, owing to its relatively slower growth, is left behind, 

 thus losing its continuity with the border of the blastoderm. 



6. I have adduced evidence of a purely morphological character for a view of 

 concrescence which is supported by the most recent experimental work. This is, 

 briefly, that true concrescence (apposition) occurs at an early period in embryo for- 

 mation. It ceases with the appearance of the caudal knob, which arises as a result 

 of the above-mentioned folding-off of the neurenteric canal. No true concrescence 



