656 The American Naturalist. [August, 
is doubled, so that we observe eight chromasomes. The 
mother-cells then divide and the chromatin is reduced to four 
rods, a second division rapidly follows whereby the chromatin 
is reduced to two rods, or half the original quantity. These 
last divisions take place by karyokinesis, but, as Hertwig points 
out, they differ from typical karyokinesis in the fact that the 
divisions follow so rapidly upon each other that the vesicular 
LAY 
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Fic. a TOGENESIS IN ASCARIS, (From prege gp Hertwig.) A, Original "E 
cell—4 chromatin rods; B, Sperm mother-cell—8 rods ; C-D neg as aa ty with 4 rods ea 
E-F, kanae a second daughter-cells, or matvre penn pen 2 rods 
resting-period of the nucleus is omitted. Thus, he suggests, 
is prevented an over-accumulation of chromatin substance 
prior to the fusion of the ovum and sperm. 
It is evident that the polar-cells are rudimentary ova, which 
do not possess the yolk-mass, etc., essential to development, 
and are divided off at a very late stage, sometimes after the 
egg has left the ovary, but are in other respects analogous to 
the spermatozoa. The reason these polar-cells have not dis- 
appeared altogether in either plants or animals is that they 
originally possessed a deep physiological importance. As the 
first polar-cell subdivides and forms two, it follows that from 
both ovum and sperm mother-cells four daughter-cells are 
