The Chromosomes of Euschistus variolarius, Euschistus servus etc. 509 
His cliagram, if assumed to be an explanation based on the facts 
of our experinients, is further in error in its illustration of the Fi hybrids. 
In his simple Mendelian scheine all the Fi hybrids are illustrated as 
typieal heterozygotes and the fact is ignored that two ont of the eleven of 
our Fl hybrids are like servus in having no spot. If such a niodification 
of the spot can be cansed by “other things in the cell”, it would 
seeni that merely caUing these “A.B.C.” is no explanation of the 
resnlts. 
Morgan excuses his attempted explanation on the gronnd that we 
have failed to explain our resnlts. We make no apology for this. We 
lielieve the duty of the scientist is to curb the natural teniptation to 
force an explanation of individual resnlts, for Science to-day is over- 
burdened by premature and undigested generalizations. We would aim 
rather to follow the example of those scientists who are willing patiently 
and conscientiously to collect data sustained by the hope that some day 
the facts inay be of value. 
Both Morgan and Doncaster dass the genital spot of variolarius 
with the secondary sexual characters of authors and they therefore 
Interpret our resnlts as not having the bearing on the theories of sex- 
determination which we Claim for them. 
Aow our Claim has been that the genital spot of variolarius is an inte- 
gral part of the male genital segment — the structure of the feniale genital 
Segment being such that the spot coulcl not be present in this segment 
without changing the form of the segment itself — and we have claimed 
that therefore a study of the transmission of the genital spot should give 
a trustworthy indication of the inethod of transmission of the entire 
genital segment. 
This Claim that the method of transmission of the genital spot should 
be an Index of the method of transmission of the genital Organs of the 
male, has been completely jiistified by further work on these hybrids. 
We quote the following from the appendix of a paper now in press (Foot 
and Strobell [14]). 
“Since this paper was finished, striking corroborative Support has 
been given to the resnlts of our experinients. In expressing to Professor 
PouLTON our desire to find an experienced Entomologist who would 
look over the parent species of our hybrids for some distinguishing cha- 
racter, (other than the genital spot) that might give additional evidence 
in Support of our experinients, Professor Poulton kindly siiggested 
Dr. Harry Eltringham of New College, Oxford. We feel very grateful 
to Professor Poulton for his interest and courtesy in this matter, and 
