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. 



L 



a 



A 



I 



Fig. 6 Compound groups formed by union of the X-chromosome with other 

 chromosomes in the Orthoptera. (a and b, from Sin6ty, 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 ; /, 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^hat outlined above is suggested by the 

 constant relation known to exist in some cases between the X- 

 chromosome and a particular pan- of the 'ordinary chromosomes/ 

 The first observed case of this was recorded by Sinety ('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 



