488 
Katharine Foot and E. C. Strobell 
(p. 17). He demonstrates a markecl difference in the relative size of 
the idiochromosomes of E. variolarius and servus in a and c of liis fig. 4. 
We have found no such difference in the individuals \ve have studied. 
IVe have not found it possible to distingiiish the two species by their 
chromosomes, and differences found in individual chroniosonie groups 
can be of no genetic value, unless they prove to be constant for the 
species. Such a differential feature would have permitted an experi- 
mental test of the individuality of the chromosomes. In Wilsox’s 
fig, 4 the Y chromosome of servus is relatively so large that it is nearly 
as large as the X chromosome of variolarius. If such a rclation existed 
in our material and wc assume a male-producing Spermatozoon, the rela- 
tive difference in the size of the XY chromosomes of the Fj hybrids 
should be conspicuously different from that of pure variolarius. If, on 
the contrary, relative size of the chromosomes is merely a structural 
feature which may be transmitted by either parent, this should be 
demonstrated by the Fi and F 2 hybrids. As our material shows no ap- 
preciable difference in the relative size of the X Y chromosomes of 
variolarius and servus we were unable to put the individuality of the 
chromosomes to this interesting experimental test. 
Our experiments, however, are quite adequate to determine whether 
either the X or the Y chromosome is necessary to the transmission of 
the genital spot of variolarius, and the experiments give evidence in no 
uncertain terms as to whether the so-called sex-determining chromo- 
somes are necessary factors in the transmission of an exclusively male 
character. They show conclusively that the genital spot oi vario- 
larius (an exclusively male character) can be transmitted 
Avithout the aid of either the X or the Y" chromosome. 
The details of Crossing variolarius X servus are published in full 
(Foot and Strobell, ’14) and the evidence demonstrated by a com- 
plete set of photographs. Briefly the results are as follows, from E. va- 
riolarms $ X E. servus o raised to maturity 11 males and 16 females 
of the Fl generation. Seven of these pairs were isolated and the offspring 
from each pair raised in separate cages. From these seven pairs of Fi 
hvbrids we raised 249 9 and 204 (^. From the back cross (Fi 9 X pure 
variolarius 0 ') 8 9 and 18 
In our preliminary report of these experiments Ave discussed recent 
chromosome theories in the light of the results of our experiments, accep- 
ting, for the sake of the argument, the assumptions invoh'ed in the theo- 
ries. IVe quote the folloAAÜng from this preliminary report: 
“Recent experimental results have caused a marked modification 
