The Chromosomes of Euschistus variolarius, Euschistus servus etc. -187 
more does not cause the cells to adhere together as in the case of 
ovarian cells. 
The work should be done under a dissecting microscope at a niagni- 
fication high enough to show the ihdividual cells. 
Descriptive. We have several hundred photographs of the chromo- 
some groups, of variolarius and servus, inchiding the soinatic chromosomes 
of both species as well as the chromosome groups of the first and second 
sperniatocytes and the first oocytes — but owing to the expense of the 
bromide print method of reproduction we have had to limit our illustra- 
tions to a few examples of the first and second spermatocyte groups. 
These groups demon- 
strate that the difference in Text figure 1. 
size between the XY chro- 
mosomes of servus is quite 
as great as the difference in 
size of the XY'” chromosomes 
in variolarius, and therefore 
the relative size of these chro- 
mosomes is not a differential 
feature of these two species — 
compare for example the 
XY chromosomes of vario- 
larius (photos 1 to 9) with 
thosc of servus (photos 10 to 
15). IVe would draw atten- 
tion to this fact because 
Wilson, ’06, found in the in- 
dividuals studied by him that the relative size of the XY chromo- 
somes of variolarius and servus was a differential feature of the two 
species. He found the difference so marked that he could distinguish 
the species by the chromosome groups. He says; “The above described 
species of Eusehistus, while agreeing precisely in the general relations, 
present individual differences so marked as to show that even the 
species of a single genus may be distinguishable by the chromosome 
groups. In this case the most interesting feature is the series shown 
in the inequality of the idiochromosomes, which beconies progressively 
greater in the series 1. E. servus, 2. tristigrnus, fissilus, 3. iciericus, 4. vario- 
larius, the inequahty in the last case being fully as great as Lijgaeus" 
Male and female Euschiatus variolarius^ showiug the black 
spot oii tho genital segment of the maleij, and the absence 
of a spot on ihe genital segment of the f«male. The 
figares demonstrate the marked difference in the form of 
the genital segment of the two sexes, showing that the 
spot could not appear in the feraale wilhout a modification 
of the entire segment. 
1) The male segment is slightly pulled out to show the entire ventral surface. 
