734 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



canal connecting it with the exterior, either in transverse or longitudinal sections; 

 but sections cannot satisfactorily demonstrate this point, the vesicle itself being evanes- 

 cent, and its walls of delicate protoplasm are so readily affected by reagents, that a 

 minute fissure is easily reduced or closed, so as to be indistinguishable. Study of 

 the living condition is therefore most reliable upon this point, and it must be observed 

 that Henneguy did make out a canal connecting the vitellus with the dorsal surface of 

 the embryo ; but he regards it as wholly independent of Kupffer's vesicle, for this latter 

 structure, he says, has disappeared some time before. But in so delicate and transitory 

 a structure as this vesicle, it is important only that its site should be regarded, and there 

 can be no question that such a posterior canal passing to the yolk beneath the embryo is 

 in communication with that site, even though the vesicle itself be no longer distinguish- 

 able. The enteric cavity at this stage is little more than a fissure between the (dorsal) 

 hypoblast and the yolk-cortex or periblast ; and Henneguy's canal can be no other than 

 the post-anal passage trending round from the dorsal groove to the under surface of the 

 embryo (that is, the surface of the yolk in Henneguy's view), and connecting the 

 transitory medullary groove, with the no less transitory primitive enteron known as 

 Kupffer's vesicle. Ryder admits that a neurenteric canal is represented, but not by a 

 tubular connection ; the solid caudal mass, where hind gut and neurula mingle, must, he 

 holds, in its axial part, represent the canal. But Ryder also noticed a fine canal passing 

 from the vesicle to the blastopore, and says — " I reserve my decision as to its true 

 nature" (No. 141, p. 527). 



Neurenteric Canal. — As the blastopore closes, a favourable side view of the caudal 

 region shows a faintly marked fissure (nee, PL III. figs. 9, 20, and 22), or rather what 

 seems to be a tubular connection of the external blastopore and the ventral surface of 

 the embryo. Unless the chamber x (PI. IV. fig. 5d), be an artificial product, the 

 tubular character is demonstrated in the section. This slight cavity curves downward 

 from the blastopore, and widens out laterally beneath the embryo (PL III. figs. 8 and 86), 

 passing for a short distance forward as a mere line marked by fine granules, and dis- 

 appearing, as Kupffer's vesicle, or the site of it, is reached. Any actual union of the 

 two vacuolated spaces is not easily made out, but the merging of the tract just described 

 and the protoplasmic wall of Kupffer's vesicle is unquestionable (PL III. figs. 20 and 22). 

 In fig. 9, PL III., the course of the canal, nee, from the corrugated blastopore, bp, forward, 

 is well seen, but Kupffer's vesicle is not yet defined ; and the relation of the two is better 

 seen in figs. 20 and 21, above mentioned, where the vesicle, kv, a minute lozenge-shaped 

 chamber, is undoubtedly related to the tract, nee, posterior to it. Certainly the passage, nee, 

 in fig. 22, is most readily, and without doubt correctly, interpreted as a neurenteric canal. 



The existence of such a canal in Teleosteans has often been questioned, and, indeed, 

 Miss Johnson amongst others declares that no such structure is known in these fishes, 

 nor an invagination giving rise to a blastopore (No. 76, p. 666); though Kowalewsky 

 is stated to have announced in an early volume of the Arch. f. Mikr. Anat. (vol. vii. 

 p. 114) such a connection of the alimentary tract with the dorsal groove in Teleostei; and 



