GLYCOGEN IN THE NERVOUS SYSTEM 455 
In sections through the entire head of ammocoets the unde- 
veloped eyes were sectioned and much glycogen found in the 
cones, no rods being present in the petromyzon eye at any stage 
of development. 
The presence of glycogen in the retinal cones of the frog was 
called attention to long ago by Ehrlich (’83), and recently there 
has appeared a paper by Brammertz (15) in which glycogen is 
asserted to be present in the retinal rods and cones of the frog, 
the pigeon, and the rabbit. 
In the adult Petromyzon and Lampetra, the eye always con- 
tains glycogen, but not in the cones. The glycogen in the func- 
tioning eye is in the retinal nerve cells (fig. 4); and very import- 
antly as it appears to me, even in the stages of advanced starva- 
tion after the spawning. Vision seems to be of the highest im- 
portance for the lamprey in the shallow streams during its 
spawning period; and that the vision is good every one will be 
willing to concede who attempts to catch them. In addition 
to the glycogen in the retina proper, the arachnoid layer of the 
eyeball near the optic nerve is filled with cells containing a 
large amount of glycogen. That is much more marked in the 
lampreys during the vegetative, or growing and maturing period 
than late in the spawning season. 
In passing, attention might be called to a very striking pecu- 
harity of the petromyzon retina. The optic nerve, instead of 
passing through all the layers of the retina and finally spreading 
out on the inside next the vitreous, only extends about half way 
through the thickness and then spreads out. As the optic nerve 
leaves the retina on its way to the brain, the fibers decussate. 
The lamprey eye certainly deserves more attention than has 
been accorded to it. 
In the course of development of Petromyzon the ova show no 
glycogen until the eggs are ripened and ready to be shed and, of 
course, immediately afterward; then the glycogen is abundant 
and scattered between the yolk granules (fig. 5). It is in very 
fine granules and especially abundant near the periphery of the 
egg. As the ovum segments, the glycogen is most marked in 
the mitotic areas of the cells, and as segmentation proceeds it 
