Literarisch-kritische Rundschau. 
The Sex Chromosomes. 
The problem of sex-determination has been examined by 
three principal methods, (1) by experiments on the influence of 
external conditions as affeeting the germ, (2) by experiments on 
the heredity of sex and of sex-limited characters, (3) by micro- 
scopical examination of the germ-cells. With reference to the third 
of these categories, at the invitation of Professor O. Hertwig, 
I will here offer a review of my ’’Studies on Chromosomes‘ and 
other papers on the subject, published at intervals during the 
past six years. It would hardly be possible to present such a 
review without including the works of many others, and especially 
those of Me Clung and of Stevens; but by reason of lack of 
space no attempt will be made to give a complete account of the 
literature. My own studies were in the first instance undertaken 
(1904) in the hope of elearing up some of the perplexing contra- 
dietions that had arisen in regard to the relations between the 
”accessory chromosome‘“ (Me Clung) and these which had been 
”called chromatin-nucleoli‘ (Montgomery) in the Hemiptera. 
These are briefly considered on a following page. 1 will here confine 
the review mainly to the conclusions reached by the work of 
Me Clung, Stevens, myself and others, regarding the called "sex 
chromosomes“, ”heterochromosomes‘‘ or ”idiochromosomes“.!) 
The essential result of these researches may be summed up 
in a few words. They have established the existence of a visible 
difference between the sexes in respect to these chromosomes, 
and have shown that it is traceable to a corresponding difference 
in the nuclei of the gametes of one sex or the other. In one 
!) The term ”heterochromosome“, proposed by Montgomery (1904) is 
now rather widely employed, despite the fact that it has been abandoned by 
its author (1906). This latter fact, and the additional one that the word 
was applied to other forms of chromosomes (the "m-chromosomes“ of Hemiptera) 
that are of quite different nature, render its continued use of doubtful 
expedieney. My own term ”idiochromosome‘“ is perhaps less open to objection; 
but I now see no reason why these chromosomes should not be called ”sex- 
chromosomes“, even though we do not yet know precisely what is their 
causal relation with sex. 
