222 E. E. JUST 
Lillie (06), too, in a most elaborate study on the egg of Chaetop- 
terus, has determined the granular structure of the cytoplasm. 
Vacuoles found in mercuric-nitrie or picro-acetic preparations 
are filled with yolk or oil in Meves’ preparations or in the living 
Platynereis egg (cf. Wilson, 798, on the cytoplasmic structure of 
eggs, including that of Nereis). 
The egg of Platynereis, as compared with that of Nereis fixed 
with the same methods, does not show so clearly the radial 
striation in the cortical layer or the homogeneous yolk spheres. 
Ten minutes after laying the germinal vesicle is breaking 
down and maturation asters, formed outside its wall, are pushing 
into its substance. The deepest of the cortical alveoli are often 
still unemptied; the whole process of jelly extrusion can easily 
be followed from its beginning in inseminated eggs. On one or 
between two of the apices of the wavy vitelline membrane the 
spermatozoon is found attached by its perforatorium. Sperm 
head, middle-piece, and tail are readily distinguished (fig. 2). 
Fifteen minutes after laying, the cortical jelly has been wholly 
extruded (fig. 3) and the first maturation spindle formed, with 
the chromosomes in late prophase. The endoplasm, with the 
extra-chromatin substance of the germinal vesicle, imbeds the 
spindle. Jn toto mounts of the egg at this stage, as is true of 
the Nereis egg, give no view of the spindle. One sees only a 
deeply stained core of substance which incloses the spindle. 
The egg is irregular in shape and the vitelline membrane is 
closely applied. 
The spermatozoon is visible on the membrane (figs. 3 and 4) 
above a group of granules similar to those more thinly scattered 
throughout the periphery of the egg. These granules are mark- 
edly like those described by Meves and are doubtless ‘mito- 
chondria;’ but in Platynereis they cannot possibly have the 
significance that Meves ascribes to them in the eggs of various 
forms. The granules appear massed beneath the point of sperm 
entry, but these masses assume no definite form. I have pur- 
posely figured those that give the nearest approach to cone 
formation (figs. 3, 4, and 5). A slender strand of cytoplasm 
may extend toward the membrane just below the perforatorium. 
