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spermatozoon, as a highly refringent spherical body. It is perhaps 
best demonstrated by the above mentioned sea water-dahlia solution ; 
but well also in the spermatozoa killed in FLEmming’s chrom-osm- 
acetic, or in platinum chloride. A dilute filtered solution of tincture 
of iodine in sea water also demonstrates it well. Treatment with 
osmic vapor brings it out very distinctly. In the case of spermatozoa 
killed by osmic vapor the nucleus after a time swells and bursts, 
leaving the spherical highly refringent centrosome and also the Neben- 
kern intact. Double staining of spermatozoa, killed in chrom-osm-acetic 
solution, or platinum chloride, with safranin and dahlia, or methyl 
green and dahlia, shows the nucleus stained red or green, the Neben- 
kern and centrosome violet. The centrosome fits closely into a de- 
pression in the anterior end of the nucleus, as mentioned above, and 
it can be mechanically separated from its socket, preserving its shape 
very well, except when treated with acetic acid reagents. In the 
Asterids examined, A. glacialis; Astropecten pentacanthus; 
Chaetaster longipes; Echinaster sepositus, the centro- 
some seems to consist of two parts; a clearer, slightly staining re- 
fringent substance, spherical in shape, surrounding a with dahlia 
deeply staining dumbbell shaped body. This latter reminds one 
strongly of the figures given by various investigators for the first 
stage of the division of the centrosome. 
This centrosome I have been able to trace from the mitosis of 
the spermatocyte, to the spermatid, and to the spermatozoon; until 
the fertilized egg it becomes the sperm centrosome figured by O. & R. 
Hertwic, BovErı and Fou. 
The Nebenkern is next in size to the nucleus; in shape it is 
generally spheroidal being flattened antero-posteriorly. It varies con- 
siderably in size in the different species, its size varying approxi- 
mately with that of the nucleus. It is usually not homogeneous, but 
containing granules of various sizes. 
The cytoplasm of the spermatid contanis a great number of 
minute granules staining darkly with dahlia, apparently identical with 
those seen in the nucleus of the spermatogone and spermatocyte, and 
which with Puatner I believe to be the remains of the mitotic 
spindle. In the development of the spermatid into the spermatozoon, 
these granules fuse gradually into larger and larger refringent bodies, 
which finally unite into a single large one, the Nebenkern. 
This Nebenkern may have in the cytoplasm of the spermatid 
_ any position whatever with reference to the nucleus; but with the 
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transformation of the spermatid into the spermatozoon it takes a 
