240 CAROLINE M. HOLT 
illustrated, was about 1350. long, while M, had 1500, anterior 
to the section, and M;, 2000u. The differences in size are 
confined to no one region but are distributed somewhat pro- 
portionally through the different layers. 
V. COMPARISON OF CELLS OF GRAY LAYER 
1. Size and number of small cells in molecular layer 
It has been the general impression that, within certain limits, 
the size and weight of the brain are indices to its functional 
capacity. In the phylogenetic series, of course, it is, with one 
or two exceptions, true that increase in intelligence is accom- 
panied by increase in the relative size of the brain. So within 
any given species of mammals, it has been assumed that the 
more efficient brain is the larger and heavier. 
The question as to whether, within such a group, increase 
in size of the brain means an increase in the number of nerve 
‘elements or in the size of the elements themselves, becomes an 
“important one. For an increase in the number of elements 
should give increased functional possibilities. ‘So, if we find in 
comparing large and small brains or divisions of brains from 
closely related animals, that the larger structure contains a 
greater number of cells and fibers, then we have reason to expect 
from the larger and more complex structure the greater degree 
of efficiency. 
If, on the other hand, the number of elements is found to be 
uniform for the part under consideration, then we must conclude 
that the large and the small brains have potentially the same 
ability to function, save as their efficiency may be affected by 
the size or degree of development of the individual elements. 
The small cells of the molecular layer (mo, fig. 2) show more 
cytoplasm; or perhaps we may say that it is possible to distin- 
guish more cells with cytoplasm in the molecular layer of large 
bulbs than of small ones. For example, the section of F; shown 
in figure 1 shows 68 cells between mitral layer and glomeruli, 
in which cytoplasm may be distinguished, while the control, 
F;, shows 158 such cells. Corresponding sections through M,, 
