310 
Charles Lincoln Edwards 
the small chromosome in 32% of the 343 fertilized bivalens eggs exa- 
amined, and Boveri (1909 b), concluded that tkis small body is an X- 
chromosome which in general may remain united to one of the autosomes. 
In the same paper Boveri announced the finaing by himself and Gulick of 
an X-chromosome in Heterakis. In my study of the spermatogenesis 
of Ascaris megalocephala (1910 a, b), I found two worms in which the 
history of the X-chromosome was followed from the spermatogonial divi- 
sions to the formation of the spermatid nuclei, and another worm from 
which the section containing the maturation divisions was lost but which 
showed the typical X-element in the primary spermatocytes. Thus in 
three out of the forty-five worms from one horse, in the series of many 
hundreds of spermatogenous cells examined, without exception the X- 
cliromosome appeared in perfect distinctness and independence. In 
Ascaris lumbricoides I have demonstrated tliat the X-chromosome is a 
multiple, in the form of a group of five components. In the course of 
studies upon other species, using methods aheady given (1910b), I found 
the number and grouping of cliromosomes in the spermatogenesis of the 
Ascaris of the cat entirely different from that described by Marcus (1906), 
for the Ascaris of the dog. This proved to be a cytological confirmation 
of the conclusion of Glaue (1909), that Ascaris canis and Ascaris felis 
are distinct species. 
In the nuclei of the first spermatocytes of Ascaris felis, shortly before 
the division, there are eight bivalent autosomes, and one pair of unequal 
chromosomes, conspicuous in size and comparable to the X- and Y-ehro- 
mosomes described in the Hemiptera and other insects (Figs. 1 and 2). 
The autosomes, for the most part distinctly tetrads, are somewliat variable 
in size but the differences are too slight to permit formulation. The 
idiochromosome pair consists of two joined together at their ends, the 
larger (X), being about double the length of the smaller (Y) 1 ). In most 
of the nuclei the two idiochromosomes show a clearly marked longitudinal 
division (Fig. 2). 
Fig. 3 presents a polar view of the equatorial plate of the first sperma- 
tocyte division and Fig. 4, a side view of the same stage in optical section. 
The idiochromosome pair is so greatly shortened while correspondingly 
thickened, that, as seen from the side, it projjects only a little beyond 
the plate of autosomes. The X-chromosome is turned toward one pole 
!) Professor Boveri (1911) is inclined to the Interpretation that this Y-element, 
taken together with an equally large piece of the X-elemcnt, represents an autosome 
pair with which is liere united as a partner an X-chromosome wlxich in other Nema- 
todes is independent. 
