The Sex-Chromosomes in Ascaris felis. 
311 
and the Y-chromosome toward the other. With the beginning of the 
metaphase (Fig. 5), both elements are again elongated and then pass to 
opposite daughter plates. 
Different views of daughter plates of the first division when they 
liave become widely separated are shown in Figs. 6 and 7. The Y-chro- 
mosome is recognized in one plate and in the other, the X-chromosome, 
twice as large as the Y, and, as a riüe, both show longitudinal division. 
Fig. 8 presents a polar view of a similar group, which belongs to a se- 
condary spermatocyte immediately after Separation from its sister cell. 
Optical sections of the equatorial plates of the second division are 
shown in Figs. 9a and b. The two cells, containing these plates, are 
firmly joined together and both spindles stand parallel, hence it is 
scarcely to be doubted that the two are sister cells. In the one plate 
a Y-element (a), can be distinguished and in the other, an X-element 
(b). Both lie with their longitudinal slits in the equatorial plane and 
now become equationally divided. Thus arise from the one, two 
spermatids with X-chromosomes, and from the other, two with Y-chro- 
mosomes. 
In the developing spermatid nuclei, the nine chromosomes are ar- 
ranged more or less clearly in a ring, in which the idiochromosome is 
visible for some time as a thickening. 
Unfortunately I have not yet been able to make a study of the ovo- 
genesis of Ascaris felis , but I think we may safely assume a condition in 
the female similar to that found by Wilson (1905a, b, c, 1906) and by 
Payne (1908), in Hemiptera and by Stevens (1905, 1908, 1910, 1911a), 
in the coleopteral genus Teneirio, and in a number of Diptera, where 
the female contains two X’s instead of X- and Y-chromosomes. Pro- 
visionally then we may accept as the formula for sex-production in Ascaris 
felis : 
a) Egg X + Spermatozoon X = XX (Female), 
b) Egg X + Spermatozoon Y = XY (Male). 
Wilson (1911b) has shown that the general result of observation 
is “that in each species all the essential relations in the distribution of 
the chromosomes conform with wonderful fidelity to the specific type. 
So true is this, that the species may often at once be identified by an 
experienced observer from a single chromosome group at any stage of 
the maturation process”. The sex-chromatin is represented in Ascaris 
megalocephala by a simplex X-element, only exceptionally free from union 
with one of the autosomes, and in Ascaris lunibricoides by a multiple 
of five X-components, while in Ascaris felis the X-chromosome is accom- 
21 * 
