DD 
(SB 
a | 
The Sex Chromosomes. 
X-class of spermatozoa are therefore formed, and all the fertilized 
eggs accordingly produce females. This is certainly a brilliant 
confirmation of the results obtained with the ordinary forms; 
and perhaps it gives a key to the variations of the sex ratios 
observed in different species. 
l have passed over many interesting details, one of which 
must be touched upon because it has caused much confusion in 
the literature; and it well illustrates the obfuscation that may 
result from a failure to distinguish between a constant and 
essential relation and the secondary phenomena by which it may 
be accompanied. This is the fact, first discovered by Henking, 
that the X-chromosome (also the Y, when present) usually remains 
throughout the growth-period of the spermatocytes in a 
compact, nucleolus-like condition, as a ”"chromosome-nucleolus“. 
Out of this grew the erroneous notion that the same behavior 
characterizes these chromosomes in the ”rest“ stages of the 
spermatogonial and other diploid nuclei. 
Though this may be true in some cases, it is certainly not 
a general characteristic of the sex-chromosomes. This is proved 
by study of the spermatogonial nuclei in many species, and also 
by study of the embryonic somatie nuclei of both sexes. Morrill 
(1910) has recently made in my laboratory a careful examination 
of these nuclei in several genera of Hemiptera (Protenor, Anasa, 
Archimerus, Chelinidea). At all stages the characteristic sexual 
differences of the chromosome-groups are clearly apparent, so 
that the sex of the embryo may readily be determined, even in 
the earliest stages of cleavage. The X-chromosome of the male 
is, however, not to be seen in any of the ”resting“ nuclei. and 
does not assume the nucleolus-like condition until the spermato- 
cytes are formed. The same is true of the X-chromosomes in 
the female diploid nuclei. In the growth-period of the oocytes, 
which I earlier examined (1905, 1906), I was unable to find a 
chromosome-nucleolus in certain genera (Euschistus, Alydus, and 
others), and this has since been confirmed by Foot and Strobell 
(1909b) in Euschistus. On the other hand, several observers 
(Gutherz, Stevens, Winiwarter and Saintmont, 
Buchner) describe in certain forms a nucleolus-like body in 
these cells, which they suggest or believe to be comparable to 
that seen in the spermatocytes. This question therefore remains 
Archiv f.mikr. Anat. Bd. 77. Abt. II. 17 
