38 
GEORGE E. NICHOLES. 
the “Daclikern” of other vertebrates. This suggested 
homology, as already indicated, I am quite unable to 
accept, for I shall show that the “Dachkern” is present 
in a scaj’cely modified condition in some primitive teleosts 
in which the torus is also present as a well-developed 
structure. 
That the ‘^Dachkern” has, so far as I can find, never 
hitherto been recognised in the Teleostean brain is doubt- 
less principally due to the fact that it has apparently 
shifted its position, and in many Teleosts is greatly reduced 
in importance, or may even have become obsolete. This 
apparent change of position is the result of the immense 
development, in Teleosts, of the tectum mesencephali 
(the anterior border of which is fixed at the posterior 
commissure), so that that part of the tectum originally 
anterior becomes inrolled to form the floor and part of the 
front wall of the optoccel, where that cavity extends forward 
above the posterior commissure. It retains, in some Teleosts 
at any rate, the condition described by Sargent (’04, pp. 188- 
189, flg. d) for adult (Ganoids, and it is remarkable that 
Sargent, who realised, and, indeed, laid some stress upon the 
forward shifting of the fore part of the mid-brain, should 
have overlooked the gi’oup of conspicuous cells which occupies 
in Teleosts a position practically identical with that of the 
“ Dachkern ” in Ganoids, and strictly comparable with that 
occupied by this nucleus in other classes of vertebrates. This 
question will be more fully discussed when we come to speak 
of the Teleosts, but in the meantime the above statement may 
be rendered more intelligible by I'eference to Text-figs. 2 
and 3. 
From what has been said it is evident that Houser’s 
observations appear to be quite in agreement with those 
which Sargent announced in his preliminary papers. In 
those papers, however, the optic reflex theory had been 
stated in the bai'est outline only, and Houser, readily 
accepting the theory, proceeded to explain and amplify it. 
Ill the result, his presentation of the facts and theory 
