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FERTILIZATION IN PLATYNEREIS MEGALOPS PPX 
valuable. For permanent preparations Bensley’s staining mix- 
tures were used. 
1. Stages previous to the penetration of the sperm. The egg of 
Platynereis rivals in structure the beauty of the Nereis egg. 
A section of an uninseminated egg (fig. 1) teased out of the. 
female directly into Meves’ fluid gives many of the details. The 
cytoplasm is sharply marked off into two regions: the exoplasm 
made up of clear cortex and zone of oil and yolk and the deeply 
staining endoplasm. 
The outer portion of the exoplasm is a mesh of pale blue deli- 
cate fibrils, the alveoli of the cortical jelly. The outer limits of 
this cortical layer—slightly more dense than the deeper portions— 
is studded with black granules immediately below the vitelline 
membrane. The inner border of the cortex arises from a zone 
of closely-packed, deep-staining bodies, from which apparently 
the walls of the cortical alveoli project. Below this inner border 
is the region of oil drops which lies in the equatorial zone, among 
spherules which prove, from their later behavior, to be yolk 
spheres, although even in the best preparations, the fine granules 
of which they are composed tend to shrink from their spherical 
walls (cf. Lillie, ’11; figure of Nereis egg fixed in Fleming). These 
yolk spheres are evenly crowded against the deeply stained basal 
area of the cortex. Around the germinal vesicle and closely 
applied to it is the endoplasmic mass, made up of fine granules 
which take the stain very tenaciously. Its outer limits are 
uneven, encroaching on the area of oil drops and yolk spheres 
as blunt projections. 
‘Seattered throughout the germinal vesicle, as in Nereis, are 
the chromosomes—fourteen tetrads. These lie among many 
black granules of varying size. Although an attempt has been 
made to study their number, distribution, etc., and to ascertain 
any constant characters, nothing now can be said further of them. 
These granules tend to be spherical and to grade down to minute 
bodies. 
The whole egg, therefore, exhibits a granular structure, both 
living and fixed, as Mathews some time since (’06) for echino- 
derm eggs and more recently Kite for some other eggs have shown. 
