678 
fibre tracts into well limited areas each with its characteristic type of 
cell structure. It is a noteworthy fact that the two types of cells 
which in a series of communications the writer has shown to be indi- 
cative of kinesodic and aesthesodic functions respectively throughout 
the higher vertebrates are here as sharply differentiated as in any 
group whatever and unusually distinctly seggregated. The kinesodic 
cell is pyramidal and provided with long processes which may be 
trace distinctly for considerable distance beyond the cell. The proto- 
plasm stains deeply and the nucleus is opaque and oval. The aesthe- 
sodic cells are flask-shaped, with short and inconspicuous processes 
and their nuclei are pale and spherical within a faintly stained cell- 
plasm. The pyramidal cells are within the axial lobe but are so 
associated with the line of attachment of the pallium and the callo- 
sum as to make it appear possible that they could be driven by 
lateral proliferation into the cortex and that such a dorsal movement 
would carry with it the callosum which latter would thus arrive at 
the place in which it is found in higher vertebrates. 
2 
Hippoeelessur® 
Comm 
Corpus 
fornicis Callosum. 
7Adix. ~ 
mesalis 
radix 
lateralis 
Precommissura 
(pers ventr) 
Fig. 2. A similar section through the same brain much farther ventrad. The sec- 
tion passes just ventrad of the anterior commissure, the position of which is indicated in 
the drawing. The position of the ental and ectal tracts in the hippocampus is shown. 
The drawing is slightly conventional. 
For a satisfactory study of the commissures of the cerebrum a 
preliminary consideration of the olfactory with its associated tracts 
is necessary. For this purpose the most satisfactory brain is that of 
the Drum (Haploidonotus). In this fish the olfactories are clo- 
sely appressed to the ventral aspect of the cerebrum or, more strictly, 
