20 J. T. CUNNINGHAM. 
wall of the intestine, or, using the term hypoblast to include 
all that part of the embryo which is concerned in the formation 
of the intestine, the inflected layer in those two types is the 
dorsal hypoblast. It is probable, therefore, that the inflected 
ring in the Teleostean is the dorsal hypoblast. It has already 
been pointed out that the whole of the inflected ring, in the 
process of the envelopment of the yolk by the blastoderm, 
comes to lie beneath the axis of the embryonic rudiment, 
between that axis and the yolk. The invaginated layer thus 
ultimately occupies the same position as the layer in the 
blastoderm of the bird to which the name hypoblast was first 
applied. I do not know of any figures of actual sections of 
pelagic Teleostean ova showing this layer between the embry- 
onic rudiment and the yolk, but it is visible more or less 
distinctly in transverse optical sections, and such sections are 
figured by Kingsley and Conn. The final proof that the layer 
in question is the dorsal hypoblast would be the demonstration 
that it formed the dorsal wall, and only the dorsal wall of the 
permanent intestine, the ventral wall being derived from the 
yolk, i.e. from the periblast. This demonstration has never 
yet been completely effected. Agassiz and Whitman (1) state 
that they have failed, as did Hoffmann and Ryder, to find any 
evidence that the periblast forms any portion of the permanent 
entoderm. The remarks concerning the development of the 
intestine in the paper of Ryder already quoted (4) convey no 
information concerning the layers from which it is derived. 
Balfour ‘Comp. Emb.,’ vol. ii, p. 61) concludes from some 
observations of his own that the gut owes its origin partly to 
nuclei derived from the yolk. It is well known that the intes- 
tine in Teleostears appears first in the greater part of its 
length as asolid cord; but it seems to me extremely probable 
that the ventral part of this cord is derived from the periblast. 
In a former paper (14) on Kupffer’s vesicle in the herring 
embryo, I described some evidence that the intestine in the 
region of that vesicle is never without a lumen, and that the 
vesicle is transformed into a portion of the gut by the con- 
version of the periblastic floor of the former into the ventral 
