EMBRYOLOGY OP THE SEA BASS. 
237 
Balfour (T. B., vol. 11, p. 268) was tlie first to make this suggestion, though iu a slightly 
different form ; for being at that time unaware of the persistence of the blastopore iu 
certain animals as the anus, he concluded that the common cavity (cloaca) was only 
established after the entire closure of the blastopore. 
It will be seen that in the interpretation of Kupffer’s vesicle I substantially agree 
with Cunningham (9)— it is the terminal part of the archenteron. Its significance is 
indeed a mere corollary of Ziegler’s general interpretation of the Teleost gastrula, but 
on its side its existence strengthens this interpretation; for the presence of such a 
(yuspicuous cavity between entoderm and periblast can only be explained on the sup- 
position that the space (virtual or real) between entoderm and periblast represents 
the archenteron. 
It only remains to speak of the neurenteric canal. Various solid cords of cells 
have been spoken of by writers, which have been construed as representing this 
canal. These cords, however, have all been very ill defined and have not been repre- 
sented in figures. Moreover, they have been found in entirely different places. In 
the Bass I have not succeeded in finding anything which could be interpreted as a 
neurenteric canal, nor do I believe that any reiiresentative of it exists. It is generally 
recognized that if the canal were present, it would open into Kupfifer’s vesicle. This 
is evident from the existence of the neurenteric streak (Fig. 82, PI. xoviii, n. str.). The 
canal could not, of course, open in front of the streak, and behind it the neural chord 
is not distinguishable from the mesoblast; or, iu other words, just behind the neuren- 
teric streak and Kupflfer’s vesicle lies the caudal mass of undifferentiated cells. It 
sometimes happens that the roof of Kupffer’s vesicle is not vaulted, but forms a 
sharply indented arch (Fig. 82). Whether the indentation seen in such individuals 
has any significance may be doubted. 
VI. NEURAL CHORD; SURFACE ECTODERM; EYE. 
Neural chord . — In the early stages the ectoderm over the entire embryonic shield 
is greatly thickened (Fig. 53, PI. xoiv) iu comi^arison with the uou-embi-yonic ecto- 
derm. This wide plate of thickened ectoderm has been called by Gotte the “axen- 
platte.” Along the middle line a thickening forms the well-known “keel,” and as 
this grows deeper the lateral parts of the plate grow thinner (the cells being used up 
in forming the keel), until there is finally a narrow deep keel passing at the sides 
directly into thin ectoderm (Figs. 57 and 58, PI. xov). This diminution iu width of 
the embryonic ectoderm and formation of a neural keel is associated with a general 
diminution in the width of the embryonic area, as may be seen in the surface views 
and on comparing Fig. 53 with Fig. 57. In the Bass, in the posterior region of the 
embryo, there is no neural furrow (Fig. 53, PI. xciv ; Figs. 54 and 56, PI. xov). In 
the brain and anterior trunk regions, howev^er, there is a well-marked furrow, into 
which the epidermic stratum sometimes dips (Fig. 58), or as often passes over like a 
bridge (Fig. 57), as has been remarked by Hoffmann (17). (Henneguy is entirely mis- 
taken when he explains the separation of the epidermic stratum from the bottom of 
the furrow, observed by Hoffmann, by supposing that the cells just beneath the epi- 
dermis were badly preserved). The neural furrow is a transitory feature, disappearing 
a short time after the stage shown in Figs. 57 and 58, PI. xcv. 
