The brain of Acipenser. 197 
rites going into the fibre layer mentioned above. These may well 
be classed with Fusari’s stellate or spindle cells whose neurites 
take the course described, and with part of my cells D. VAN GE- 
HUCHTEN says that the neurites of all these cells are directed la- 
terally. In Acipenser I find some of them going mesially from their 
cells to cross in the dorsal decussation. 
4) Large bipolar cells horizontally placed near the periphery. 
These correspond to cells in the same position in Acipenser, but 
were apparently not found by Fusart. 
| SAUERBECK (96) describes in the tectum of Selachians 1) greatly 
expanded but slightly branched cells in the middle layer, 2) spindle- 
shaped cells with slightly branched dendrites directed toward the 
external and internal surfaces, 3) tangentially disposed cells in the 
outer layer. 
F. Mayer (97) finds three layers in the tectum of Ammocoetes, 
of which the two outer layers are destitute of cells. The external 
layer contains optic fibres and fibres destined to the decussatio 
transversa. The middle layer is made up of the end branches of 
optic fibres and the dendrites of cells situated in the inner layer. 
The inner layer contains three kinds of cells: cells with single 
dendrites whose neurites go to the tractus tecto-bulbaris, posterior 
commissure, or the dorsal decussation to end on the other side; 
bipolar cells whose neurites go via the decussatio transversa to the 
cortex; and collossal cells. MAYER does not describe cells of the 
II type, nor cells giving rise to centrifngal fibres in the optic nerve. 
These are doubtless to be found among his cells of the first kind. 
It is interesting to know that the fibres to the fore brain come 
from the bipolar cells. The same may be the case in Acipenser, 
but the small size of the bundle to the fore brain, if it be such, 
makes it difficult or impossible to determine the origin of the fibres. 
In higher forms there are many more bipolar cells, including prob- 
ably several species of cells, so that it will be difficult to identify 
the cells which give rise to the fore brain bundle in different 
Vertebrates. 
Three papers have appeared from the brothers CAJAL on the 
subject of the optic lobes, two of which I have read, S. Ramon Y CAJAL 
(91) on birds, and P. Ramon y CAyAL (94) on Amphibians and 
Reptiles. $S. Ramon recognizes in birds fifteen layers which for 
the most part correspond to zones described by STIEDA. P. Ramon 
recognizes fifteen layers in Rana, ten layers in Reptiles, and (judging 
