OLFACTORY CENTERS IN TELEOSTS 239 
commissuralis lateralis and nucleus entopeduncularis. The fiber 
connections of several of these nuclei are still very imperfectly 
known and their morphological interpretation should therefore 
be considered purely provisional until this knowledge is extended.! 
III. DISCUSSION 
The structural plan of the teleostean diencephalon and telen- 
cephalon is very different from that of any other vertebrate type 
excepting the higher ganoids (notably Amia); but as we follow 
down the phylogenetic series through the lower ganoids to the 
generalized fishes, we approach progressively nearer to the com- 
mon vertebrate type. When the development of the teleostean 
brain is more fully known it will probably prove easy to follow 
here also the sequence of form changes from a generalized type. 
It is generally accepted that the primitive form of the verte- 
brate central nervous system was a simple epithelial tube and that 
from its rostral end two pairs of lateral vesicles were evaginated. 
One of these comes from the diencephalon to form the optic ves- 
icles: the other comes from the telencephalon to form the cere- 
bral hemispheres. The telencephalon must be defined, as taught 
by His and Johnston, as the rostral segment of the neural tube, 
including the hemispheres evaginated from it, and not as the hemi- 
speres alone, as in the BNA tables. 
There is the greatest diversity in different vertebrate types 
in the relative amounts of the telencephalic segment which are 
evaginated into the hemispheres, but in no case is the whole of 
this segment represented in the hemispheres. Accordingly, 
we subdivide the telencephalon into telencephalon medium and 
! Johnston’s still more recent paper on the telencephalon of ganoids and tele- 
osts (Jour. Comp. Neur., vol. 21, no. 6, December, 1911), appeared while this con- 
tribution was in press. His results differ in some matters of fact and in several 
matters of interpretation from my own. So far as these concern the somatic or 
non-olfactory connections, they do not fall within the scope of this article. Some 
of his morphological conclusions J] think rest upon an incomplete knowledge of 
the anatomical facts; but since the homologies of the telencephalic and dien- 
cephalic centers in the carp and other lower vertebrates will be fully discussed in a 
forthcoming paper, Johnston’s conclusions will not be further considered at this 
time. 
