The Sex-Chromosomes in Ascaris felis. 
ßy 
Charles Lincoln Edwards. 
(Froin the Zoological Institute. Würzburg.) 
With plate XXVIII. 
In spite of the belief of some authors that sex-chromosomes do not 
exist, and of the objections of others against the theory that these bodies 
are sex-determinants, the facts now demonstrated in various Orders of 
insects, in Nematodes, sea-urchins (Baltzer 1909) the opossum (Jordan 
1911), the gidnea-pig (Stevens 1911b), and man (Guyer 1910), can scarcely 
admit of a doubt of the essential relationship of the idiochromosomes to 
the production of sex. While skeptical “that particular chromosomes 
alone are sex-determinants“ Montgomery (1910) makes the general 
admission that “In all probability the activities of the chromosomes are 
influential in estabhshing sex, but not in the crude way in which the 
process has been imagined”. Morgan (1909) beüeves that the idiochromo- 
somes “may follow sex or be associated with other differences that deter- 
mine sex, rather than be its sole cause”. It may be some time before we 
know about the final causation of sex and consequently, for the present, 
it is rational to agree with Wilson (1911a), that the sex-chromosomes 
constitute “one Unk, probablv an essential one, in a chain of factors by 
which sex is determined and inherited”. 
The presence of sex-chromosomes in Nematodes has been established 
by work done in the Zoological Institute, Würzburg within the last two 
years. The occurrence of a small chromosome in Ascaris megalocephala 
l'valens was noted by Herla (1894) and Boveri (1899) and again found 
by the latter in 1908 in a large number of fertilized eggs of different fe- 
males. Boring (1909) who made a careful study of this material found 
Archiv f. Zellforschung. VII. 21 
