72 MEMOIRS OF THE NEW YORK ACADEMY OF SCIENCES 



There is no evidence, however, that HENNEGUY attributed any such significance to 

 this last phenomena as has been done by KOPSCH and myself. 



JABLONOWSKI ('98) offers a view based largely upon that of KOPSCH, though not 

 identical with it. He regards the first formed section of the embryo as resulting 

 from an " excentrischer Zusammenziehung " of the blastopore lips, comparable to 

 that described for Amphioxus by HATSCHEK. After the definite establishment 

 of the embryonic body (he seems to have in mind the appearance of the caudal 

 knob) growth occurs "through multiplication of material situated in the Endwulst." 

 The latter represents only the anterior (dorsal) wall of the neurenteric canal, which 

 is thus, properly speaking, an "incisura neurenterica" (His) like that of the early 

 elasmobranch. In favor of this view he cites the artificially produced bifid condi- 

 tion above described. JABLONOWSKI, accordingly, recognizes no detachment of the 

 neurenteric canal from the rest of blastopore. Neither JABLONOWSKI nor KOPSCH 

 hint at any relation between neurenteric canal and Kupffer's Vesicle. 



Conclusions. From the previous discusion, it is evident that I have been led, 

 on purely morphological grounds, to a view of the formation of the fish embryo in 

 full accord with the results of the latest work in the experimental field. The neur- 

 enteric canal I have shown, moreover, to be much more than an "ideal" structure, 

 it having, in some cases at least, an open lumen, and being in others represented 

 by a solid ingrowth of cells. Of course, such a neurenteric canal as occurs in Am- 

 phioxus is impossible in any teleost, owing to the solid condition of the neural axis. 



That the process cf concrescence, which leads to the formation of the neurenteric 

 canal, was previously instrumental in the construction of the embryonic body an- 

 terior to it seems to be proven by KOPSCH'S experiments, although he rejects the 

 word "concrescence" in this connection. He admits, however, an apposition of the 

 two laterally situated halves, which is all that is necessary for the present discussion. 



The long-continued emarginate condition at the caudal end of certain embryos 

 (see above) leads me to the belief that the process of concrescence is one of con- 

 siderable duration, and the fusion of the germ-layers along the embryonic axis 

 ("primitive streak") in front of this point, gives further evidence of such a process. 

 (JABLONOWSKI also regards this region as due to "Nahtbildung.") That concrescence 

 (apposition) ceases, however, with the formation of the neurentoric canal is certain. 

 That it is thereafter replaced by a process of confluence seems proven by the experi- 

 ments of both Morgan and Kopsch. [Also by my own. See Supplement.] 



