Some Problems of Reproduction: a Comparative Study of ...

SOME PROBLEMS OF REPRODUCTION. 58
and both are nieces of the first polar body. I append a schema
to show these relations (Kg. 9). 1
No
Fie. 9.—i. Schema to show usual formation of polar bodies in Metazoa.
ii. Schema of polar bodies iu Ascaris.
Unmistakably these processes point to a primitive condition,
when each ovarian ovum divided in two stages to form a brood
of four oospheres. Unfortunately the phenomena of the
gametogenic bodies have been made too much a study isolated
from other similar formations, and false interpretations have
been put on the peculiarities of their mitoses to suit preconceived
ideas. Doubtless had the segmentation of the Metazoan egg
proceeded after the type of Cystoseira (supra, p. 17), ingenious
hypotheses would have been framed to explain what
plasmic properties resided in each of the seven nuclei rejected,
and for what reason each one had to be expelled from the egg
to leave a pronucleus fit for fertilisation.
The remarkable uniformity of oogeny (in the restricted
sense) in the Metazoa as compared with other equivalent
groups is perhaps attributable to the fact that its processes
are usually limited to the short time during which the ovum
is free before fertilisation, and to the fact that it is usually
free at that time: a uniformity of external conditions has
preserved uniformity of results. The much greater variability
of spermatogeny which takes place under much more varied
conditions supports this view. 2
1
Blochmann has found in some Insects that the second polar body divides,
but not the first (" Zahl d. B.iclituugsk6rper,'.&c," in ' Morph. Jahrb.,' 18S9).
s
I have omitted the consideration of " paracopulation " iu the "winter
eggs" of Cladocera, as described by Weismann and Ischikawa (in ' Zool.
Jahrb.,' "Abtheil f. Anat. u. Ontog. d. Thiere," iv, pp. 155—196), In