GLYCOGEN IN THE NERVOUS SYSTEM 457 
tation proceeds and the germ layers are formed it is present in 
all germ layers but is especially marked in the neural plate. 
Glycogen appears in the first proton or anlage of the eye, ear, 
and nose; in the brain and the myel (medulla spinalis) and in all 
the organs and tissues of the embryo; that is, in Amblystoma 
glycogen is universal in its distribution throughout the body in 
the early embryonic condition, but the liver early takes on the 
most prominent glycogenic function. It persists for a long time, 
perhaps throughout life in the cardiac muscle and in the retina 
(rods and cones). 
GALLUS DOMESTICUS 
In the chick glycogen appears first in the cardiac muscle, 
thirty-sixth to the forty-eighth hour of incubation. In strong 
contrast with Petromyzon and Amblystoma, the appearance of 
the glycogen in the nervous system is late. In the sixth to the 
tenth day, it is very abundant in the medulla oblongata and in 
the sacral and lumbar myel (medulla spinalis). 
In the tenth day it appears in cartilage and in the muscles of 
the trunk and limbs, but it is not so abundant in the somatic 
muscles of the chick as.in those of Petromyzon and mammalian 
embryos., It is also present, to a limited extent, in the epidermis 
and the enteric epithelium. 
It has already been pointed out by many previous workers 
that glycogen is not so abundant in the organs and tissues of the 
chick as in the embryos of many other forms, including mammals. 
It seems to me that this is true if one deals with the glycogenesis 
in all of the organs at any one period. With the large amount of 
stored food in the hen’s egg, the chick has the advantage of devel- 
oping at leisure, so to speak, and whenever the time arrives to 
bring to definitive form or activity any tissue, the glycogenic 
builder and energy producer is on hand, but as these perfecting 
processes do not occur in all the organs and tissues of the chick 
practically at the same time as with Amblystoma, one finds abun- 
dant glycogen at any one period only in a limited region of the 
body. 
