PLATE 1 
EXPLANATION OF FIGURES 
1 Spermatozoa of Nereis from preparations fixed in Gilson’s fluid and stained 
in safranin and Siiure-violet. la, the entire spermatozoén; 1b and 1c show the 
excentric attachment of the tail to the middle piece; 1 d, basal view of the sperm- 
head showing ring-shaped middle piece and attachment of tail. h.c., head-cap; 
m.p., middle-piece; p, perforatorium. It may be noted here that the form of the 
perforatorium in the living spermatozoén is more like the spike of a helmet. 
2a,2b,2c :From three eggs fifteen minutes afterinsemination. The entrance 
cone is well developed and stains dark, homogeneous. The perforatorium has 
pierced the membrane, at least in 2a and 2c, but is not embedded in the cone. Note 
variations in appearance of the middle-piece. ‘Tail not seen. 
3.a,3b From two eggs twenty-seven minutes afterinsemination. Theconeis 
retracted, but stains as before. The perforatorium stains more strongly than in 
fig. 2, but it has not yet entered the substance of the cone. The tails were very 
distinctly seen in these preparations. 
4 Thirty-fourminutesafterinsemination. The perforatorium has now entered 
the substance of the cone, and granules are beginning to appear in a smaller 
lighter area of the cone surrounding its tip. 
5 a,5b From two eggs thirty-seven minutes after insemination. The clear 
space in the cone is now larger and the granules at the tip of the perforatorium 
more numerous; 5 a, from an almost tangential section, so that the vitelline mem- 
brane was obscured. Note thedouble perforatorium; 5 b, middle piece shows no 
granules; cf. 2 b. ; 
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