IOWA ACADEMY OP SCIENCES. 
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body from which three or four dendrites radiate indifferently 
in every direction. The dendrites do not branch very much, 
but there are so many of them that a very tangled complex is 
given. 
In the mid-brain the ependyma cells are highly developed. 
Their processes run straight out through the whole of the 
nervous matter, giving a characteristic appearance to this part 
of the brain. The nerve cells appear to be somewhat better 
differentiated than in the fore- brain. Near the outer surface 
there are cells which send their dendrites in a tangential course. 
At a deeper level there are somewhat larger cells whose 
dendrites spread out in all directions. Still another type of 
cell may be found having long dendrites passing over the 
greater part of the distance between ependyma and outer sur- 
face. 
The cerebellum has a structure which appears to foreshadow 
in its general plan the details of structure of a higher brain. 
It has a series of well defined layers, and the same layers are 
present in the same relations to each other as are found in the 
human cerebellum. There is a wide nuclear zone lying next 
the ependyma. A molecular layer lies next the outer surface. 
Between the two there is a crowded row of Purkinje cells. 
These cells have the familiar dendrites forming an arborization 
in the outer zone, but the degree of branching of the dendrites 
is far less marked than in the mammalian cerebellum. 
The medulla oblongata exhibits a most beautifully reticulated 
system of fiber tracts. In this reticulum the microscope reveals 
neuroglia cells, processes of ependyma cells, and an occasional 
nerve cell. Whether the nerve cells are present except in con- 
nection with the nuclei of the cranial nerves which arise here 
is a fact which I have not yet determined. 
Summarizing the above results, we see that mid-brain, cere- 
bellum, and medulla oblongata foreshadow in organization the 
human type; but that the fore-brain does not. Coupling this 
fact with the suggestion to which I have already alluded as to 
the significance of the dorsal eminences of the fore-brain, and 
we have grounds for the hypothesis that the cerebral cortex 
proper is of secondary development. 
