The Chromosomes of Euschistus variolarius, Euschistus servus etc. 493 
is seen in servus and in the and F 2 hybrids. In the thread-like chro- 
mosomes of the ernbryos the constriction frequently occurs at quite a 
definite point in one or both members of a diploid pair and frequently 
more than one pair show like constrictions or small detached portions 
which appear as independent chromosomes. "WTiether such appearances 
(which are present in both sections and smears) are normal, or patho- 
logical, or due wholly or in part to the technique, we have not been able 
to determine. 
The X Y chromosomes and the genital spot. 
If the transmission of the genital spot is dependent upon the pre- 
sence of either the X or the Y chromosome this should be determined 
by our breeding experiments, in which we have crossed two species of 
Hemiptera — the genital spot being present in one species and absent 
in the other. A necessary step in determining this point is an analysis 
of the chromosomes based on the current assumptions as to their beha- 
viour in the maturation divisions. We have attempted to illustrate the 
first and second divisions of the spermatocytes by a simple diagram (text 
fig. 2) in which we have used the methods of designating Univalents by 
the letters of the alphabet, bivalents being represented as AB— CD— EF. 
First Sp. Cyte 
Cbromosomes. 
ABCDEFXY< 
Text figure 2. 
Sp. Tid. 
CItromosomes. 
Second Sp. Cyte 
Chromosomes. C E X Q 
.ACExy< 
^'A C E Y — (3 
/B D F X — Q 
^BDFxy/ 
\ 
BDFY (3 
Scheme of the two maturation divisions of Euschistus variolarius and Euschistus servus based on 
the assnmption tbat tbe iirst maturation division separates autosomes of maternal and paternal origin 
and tbe second division balves tbem. Tbe XY cbromosomes on tbe contrary being balved in tbe 
first division and separated in the second division. Tbe relative positions of the autosomes may le 
changed nnless definite cbromosomes are always destined to the same pole, but reversing their position 
in this regard does not alter tbe end result— tbat tbe only chromosome common to both so-calied 
male-producing spermatids is the Y chromosome'). 
The above diagram illustrates the important point that on the above 
assumption as to the maturation divisions the Y chromosome is the only 
1) For the sake of simplicity only six of the 12 autosomes are designated. 
