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I A Study of Chromosomes and Chromatin Nucleoli in Euschistus crassus. 55 
I biit this e^^dellce may be of interest merely because it is out of harmony 
witli certain theoretical considerations. 
If tlie plane of division is a matter of fundamental importance for 
the X and Y chromosomes, logically the plane of dmsion of ordinary 
chromosomes should receive equal consideration and this leads us to 
conclusions that appear to be inconsistent Avith certain hypothetical 
assumptions. 
If the first division of the ordinary chromosomes separates so-called 
pure male and female Univalents then the two sister ceUs (second sperma- 
tocytes) must always have unlike ordinary chromosomes — unlike as 
to these chromosomes while they are alike as to the X and Y chromo- 
somes. 
If we express this difference by the usual method of designating 
“univalents” by the letters of the alphabet, we may say that one sister 
second spermatocyte of Euschistus crassus can have A. C. E. G. I. X. 
Y. and the other sister second spermatocyte B. D. F. H. J. X. Y. 
These relations can be changed unless definite chromosomes are always 
destined to the same pole; but reversing their positions in this regard 
does not alter the end result — that the sister cells of the fii'st division 
are always unlike as to the ordinary chromosomes. The second division, 
on the contrary, gives two sister ceUs (spermatids) that are alike as to 
the ordinary chromosomes but unlike as to the sex chromosomes. FoUow- 
ing the above formula, the 4 spermatids resulting from the two matura- 
tion divisions may be as follows: One of the two so-caUed female pro- 
ducing spermatids may have chromosomes Ä. C. E. G. I. X., and the 
other female producing spermatid B. D. F. H. J. X. One of the two 
so-caUed male producing spermatids will have chromosomes A. C. E. 
G. I. Y. and the other male producing spermatid B. D. F. H. J. Y. 
In Order to keep this relation constant for every quartette of spermatids, 
it is necessary to assume that in both divisions definite chromosomes 
always go to a definite pole, though as stated above reversing them po- 
sitions cannot alter the end result — that the spermatids of the same 
sex are unlike for the ordinary chromosomes. Thus if we are looking 
for a chromosomal difference between the male and female spermatozoa, 
we find it much more pronounced between the two spermatids of the 
same sex than between the two of the opposite sex. 
We may juggle the chromosomes as we will, but as long as it is 
assumed that the first division separates pure male and female univalents 
and the second division halves them, the above conclusion seems in- 
evitable. And further, if the pretension is made that any one of the 
