92 EDMUND B. WILSON 
the female homozygous. The puzzle of the Y-chromosome 
would thus be solved; for although a separate Y-chromosome, 
when present, is confined to the male line, its disappearance 
only reduces the male from a homozygote to a heterozygote in 
respect to the Y-chromatin, and the introduction of supernumer- 
ary Y-chromosomes into the female (as in Metapodius) brings in 
no new element. 
Fig. 6 Compound groups formed by union of the X-chromosome with other 
chromosomes in the Orthoptera. (aandb, from Sinéty, the others from McClung. ) 
a, triad group; first division of Leptynia, metaphase; b, division of similar triad in 
Dixippus; c, triad group formed by union of the X-chromosome with one of the 
bivalents, first spermatocyte-prophase, Hesperotettix; d, the same element from 
a metaphase group; e, the same element in the ensuing interkinesis; f, the com- 
pound element of Mermiria, from a first spermatocyte prophase; g, the same ele- 
ment in the metaphase (now, according to McClung, united to a second bivalent 
to form a pentad); h, the same element after its division, in the ensuing telophase. 
The same general view as that outlined above is suggested by the 
constant relation known to exist in some cases between the X- 
chromosome and a particular pair of the ‘ordinary chromosomes.’ 
The first observed case of this was recorded by Sinéty (’01) in 
the phasmid genera Leptynia and Dixippus (fig. 6 a, b), where the 
X-chromosome is always attached to one of the bivalents in the 
