The brain of Acipenser. 233 
lar zone. Viewed in this way, the olfactory tract in Reptiles loses 
its complex composition and becomes comparable to that of other 
Vertebrates. EDINGER’s description of the lobe implies that he 
regards the internal cellular zone (“Lobus cortex”) as a forward 
extension of the area parolfactoria and hence as belonging to the 
fore brain proper, rather than to the olfactory lobe. How this 
relation would come about is difficult to see, and the fact that this 
conception would deprive the lobe entirely of the layer of granule 
cells which is constant in all other Vertebrates seems to me to be 
a fatal objection to it. 
The relations of the peripheral processes of these cells is a 
difficult problem which requires further investigation. In lower 
Vertebrates (Acipenser, Petromyzon, Rana) they are long, slender, 
widely expanded, not profusely branched, not conspicuously marked 
with spines, and very little thickened when they enter glomeruli. In 
Mammals they are not widely expanded and have not been traced 
quite to glomeruli. In the absence of complete investigations on 
the intermediate forms, especially Reptiles, it is impossible to know 
whit change has taken place in the relations of these peripheral 
processes. In view of the apparent absence of neurites from the 
granules in Mammals, it is possible to suppose that a large part of 
the cells in the granular zone in Acipenser have lost their connection 
with glomeruli and have ceased to transmit impulses to the fore 
brain. On this hypothesis they must serve connective functions 
(glia, KOLLIKER) although they do not resemble the glia in other 
parts of the brain. VAN GEHUCHTEN & MARTIN have described 
glia cells side by side with the granules. Such a change of function 
as this hypothesis implies seems very improbable. It is possible 
that some of the cells of the granular zone in Acipenser have come 
to lie nearer the surface in Mammals and are reckoned with some 
of the varieties of mitral cells or “kleine Pinselzellen”. There is 
much greater variety among these cells in Mammals than in Aei- 
penser and it seems scarcely possible that the large stellate cells in 
Acipenser with their widely expanded dendrites should become re- 
duced to the typical granules of Mammals. The smaller stellate 
cells of the glomerular zone may be compared with some of the 
superficial ‘‘Pinselzellen”. The peculiar “cells of CAJAL” in Aci- 
penser can not at present be compared with known cells in Mammals. 
On this second hypothesis there remain a large number of cells of 
undoubted nervous character in Acipenser (granules, spindle cells, 
