DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 735 



Kingsley and Conn refer very briefly to what they style a " neurenteric canal," of 

 which they give a figure (No. 78, fig. 30, pi. xv.). Raffaele also recently alluded to it 

 in Uranoscopus (op. cit., p. 28). That it has been rarely observed, and never fully 

 described, is probably due to its evanescent character, and it may in some cases, indeed, 

 never be developed. Balfour and Deighton (No. 19, p. 185) speak of it as "that 

 most variable structure in the chick," and the same description may be applied to 

 it in the Teleostean ovum. This canal can hardly be due to the supposed process of 

 concrescence, as it has not the character so much of a vertical fissure as a depressed cavity 

 passing obliquely downward and forward between the embryo and the yolk, and is best 

 seen in transverse or side view. It is, indeed, less of a tubular canal than of a tranverse 

 fissure between the convex embryonic surface and the concave yolk-surface, and opening 

 externally by the blastopore. In PI. III. fig. 8, in the living condition its course is 

 clearly indicated, the shallow dorsal groove continuous with the blastopore indenting 

 the caudal region, and then merging in the descending tract, nee, which widens out and 

 becomes lost in the mass of periblastic protoplasm, kv, in which Kupffer's vesicle 

 makes its appearance. Sometimes this neurenteric passage connecting the neuro- 

 chordal groove above and the enteric region below is a distinct interspace (PI. III. fig. 

 9, and possibly nee? PI. IV. fig. 5d). It is often marked by granules (PL III. fig. 

 22), or even a tract of undifferentiated protoplasm, in which two or three clear spheres 

 are imbedded (PL III. fig. 20). Fig. 8, PL III., for instance, showed this last named 

 condition at 10 a.m., with a connecting tract opening externally between the closing lips 

 of the blastopore. An hour and a half later, a spindle-shaped plug (PL III. fig. 8a) 

 sending outward an acuminate process, interrupted the canal, nee, and presented 

 amoeboid movements. The plug then coalesced with the margin of the blastopore, and, 

 assuming a distinctly granular appearance, formed a bridge across the fissure connected 

 with the inferior tract (fig. 8c). # Meanwhile, the clear vesicles mentioned above had 

 enlarged, and finally coalesced to form Kupffer's well-known structure. Such a plug 

 as we have described Balfour and Deighton noted in the chick, and they speak of a 

 mass of rounded cells pushed up through the neurenteric canal (No. 19, p. 186). The 

 phenomenon just detailed shows two important points, viz., the connection of the 

 external blastoporic orifice with the region of Kupffer's vesicle, if not with the actual 

 structure itself, and the obliteration of the passage of connection, i.e., the neurenteric 

 canal, by a plug probably pushed up from below. 



The section figured in PL IV. fig. 5d, and already referred to, passes through the 

 precise region we have been dwelling upon, and a few loose cells alone obstruct the 

 connection of the dorsal and ventral (enteric) groove, ne. The section is interesting as 

 showing a portion of Kupffer's vesicle, or the groove itself imbedded in a thick layer of 

 periblast, per, as we have before described. 



Now the sections figured (PL IV. figs. 5b-5d, and fig. 6) clearly show the continuity 



* Fig. 86 is an intervening stage, when neither plug nor connecting bridge are visible. 



