218 E. E. JUST 
1. Insemination. In Platynereis insemination normally takes 
place in the body cavity ( Just, ’14). The eggs, when laid, 
have the sperm attached within a thin hull of jelly, the secre- 
tion of the cortical layer. If the worms be allowed to deposit 
eggs in India ink ground up in sea-water it can be proved satis- 
factorily that a hull of jelly, as in Nereis, envelops inseminated 
eggs. This jelly, absent in uninseminated eggs, is formed from 
the exoplasm of the egg as the result of stimulation through 
sperm attachment. In sea-water the zone between India ink 
particles and the vitelline membrane gradually widens, not so 
much because of the slow diffusion of the jelly from the egg, as 
because of the swelling of the extruded jelly. 
_ Insemination in some way brings about oviposition. The 
presence of the sperm in the female is a stimulus to egg laying; 
as in Nereis (see Lillie and Just) the presence of the sperm in 
the sea-water brings about the shedding of the eggs. The first 
result of the attachment of the sperm to the egg is jelly formation 
through cortical secretion, with the consequent formation of the 
perivitelline space; and this process must begin in the body 
cavity, since eggs have a thin jelly investment when laid. As 
in Nereis the vitelline membrane is preformed; the sperm does 
not cause ‘membrane formation.’ 
For twenty to thirty minutes after oviposition, the sperm 
remains external to the egg. During this time profound changes 
take place in the egg, many of which doubtless are to be inter- 
preted as changes incident to maturation, the mechanism of 
which is released with the breakdown of the’ cortical substance 
and the consequent formation of the perivitelline space. These 
changes: breakdown of the germinal vesicle, formation of the 
spindle, polar body formation, and cytoplasmic movements, are 
easily followed in the living egg. 
2. Penetration. In Nereis a striking phenomenon of sperm 
attachment is the fertilization cone (Lillie, ’11, 712). In Platy- 
nereis no sharply defined cone is found. There are, however, 
cytoplasmic disturbances at the point of sperm entry. In 
polyspermic eggs the cytoplasm may form a low blunt protrusion, 
with as many as five spermatozoa attached to it, but this is not 
