28 THE ENTOMOLOGIST. 
Further, the angular prominences and curved excisions, so 
strikingly evident in quercinaria, are merely represented by a 
very gentle projection of vein four and a consequent tendency 
to a single excision above. The coloration, etc., of quercinaria 
are too well known to permit of their being described here. 
Cross-Patrine. 
These two species very early attracted my attention as 
possible subjects for hybridity experiments, and I therefore 
obtained a small supply of EH. subsignaria ova from Montreal 
during the big migration some years ago. From these I reared a 
fair number of imagines, and thus secured a goodly supply of 
ova for the following year, and these I reared with H. quercinaria. 
Both insects fed on hawthorn and at equal rates; they thus 
emerged and were in my cages at the same time. The insects 
paired just after dusk, and the pairings only lasted for a short 
time. ‘Two days after emergence ova, which, to judge from their 
regularity in laying and their non-glossy appearance, seemed 
to be fertile, appeared in the subsiqnaria 3 X quercinaria 2 
cage. In the case of the reciprocal pairing, small batches of 
ova laid irregularly were deposited by the subsignaria female; this 
irregularity in hybridity work is a sure sign of infertility, and the 
opinion, formed then, was justified, for, whilst the ova obtained 
from the first-mentioned pairing overwintered safely and duly 
yielded their larve, not a single larva resulted from the reciprocal 
cross. Experiments, repeated hundreds of times, have had the 
same result; the subsignaria ¢ x quercinaria 2 cross is always 
fertile, whilst the reverse is always sterile. I do not think that 
the cause is due to any lack of ability of quercinaria spermatozoa 
to fertilise subsignaria ova; on the contrary, the cause of the 
failure is mechanical and depends on the size of that peculiar 
guiding organ called the Furca (vide figs. la, 2a, and 3a) 
developed in the Hnnomids and their allies for introducing the 
penis through the ostiwm into the Ductus burse. The organ 
in subsignaria (fig. 2a) is broad and stout, and is able to open 
the Ductus to allow of the correct placing of the spermatozoa 
in the Bursa copulatric. On the contrary, the Furca in quer- 
cinaria (fig. 1a) is long and narrow, and is unable, owing to 
its length and narrowness, to displace the thick chitinous Ductus 
burse sufficiently well to allow of the act of fertilisation. 
Little need be said of the hybrid larve ; they were practically 
the mean of those of the parents, except that they leaned in the 
colour, both of head and body and possibly in the general 
structure of the warts and tubercles, to the male parent sub- 
signaria, a result to be expected if, as I argued, that species 
is phylogenetically the older form. The pup were quite 
normal and very like those of subsignaria, and yielded the 
imagines about the usual time of the parents; if anything, 
