362 FRANK R. LILLIE 
and a subjacent membrane or layer, about 6-7u in thickness, 
which he called the zona radiata. As will appear from the sequel 
however, the latter is not a membrane in the usual meaning of 
the word, but a cortical, coarsely alveolar layer of the egg. It is 
transparent and somewhat granular, and the granules tend to be 
arranged in radiating lines. There is no perivitelline space in 
the unfertilized egg. 
In sections of unfertilized ovocytes fixed in Flemming’s fluid, 
the zona radiata is seen to be a coarsely alveolar layer with 
homogenous alveolar contents (fig. 1). The walls of the alveoli 
are continuous internally with the p:otoplasm of the egg, and 
unite externally to form a protoplasmic layer applied to the 
vitelline membrane. The alveoli are closed externally (figs. 
1 and 2). The zona radiata is in fact a coarse emulsion or foam- 
structure. 
Unfertilized eggs of Nereis are entirely devoid of jelly and they 
lie in immediate contact in the sea-water. If India ink be ground 
up in the water, the particles come in contact with the vitelline 
membrane. Each fertilized egg, on the other hand, is surrounded 
by a thick layer of colorless transparent jelly; If many eggs are 
contained in the dish, fusion of the contiguous gelatinous mem- 
branes binds the eggs into a mass; the cortical layer (zona radiata) 
is absent in fertilized eggs, and there is a narrow perivitelline 
space between the vitelline membrane and the surface of the egg 
(fig. 3). 
The jelly is formed by the extrusion, or diffusion, of the alveo- 
lar contents of the cortical layer through the vitelline membrane; 
- the egg of Nereis, in fact, secretes its own Jelly, as may be readily 
demonstrated in life by inseminating under the microscope with 
excess of sperm. If the sperm be added to closely placed eggs 
and a cover glass applied so as to force the eggs into a single 
layer, and the preparation examined with no loss of time, the sperma- 
tozoa will be seen in large numbers in contact with the vitelline 
membrane. In one or two minutes the spermatozoa are moved 
away from the surface of the membrane by some invisible repel- 
ling substance, and, if the eggs be numerous, the spermatozoa 
unite in three to five minutes to form lines that bound hexa- 
