Hybridising T. bistortata and T. crepuscularia 35 
delamerensis from various Scotch, Irish, Welsh and English 
localities in my own collection. 
I have, as much as possible, neglected the use of the 
term “intermediate.” It appears to me that it is frequently 
most carelessly used, and, as generally applied, comprises 
almost anything from a sort of ‘“ piebald” mixture, so to 
speak, of two species, to the general resemblance a hybrid 
must bear to both parents, according as we study them 
from the point of view of one or other of the parents. 
All the hybrids dealt with in this paper are, with here 
and there an exception, in varying degrees, intermediates, 
i.e. almost every specimen appeals, in some part of its 
facies, to a specialist as resembling 7’. bistortata, whilst 
the same specimen, in other particulars, strikes one as 
resembling 7’. crepuscularia, Even the (approximately) 
black specimens, which, from their striking coloration, 
naturally most conceal any approach to 7’. bistortata, are 
distinctly modified in general appearance and wing struc- 
ture, and show a tendency to the more marked sexual 
differences apparent in wild 7’. bistortata. There is also 
another difficulty which the introduction of 7. ab. dela- 
merensis has caused. In nature, specimens of this aber- 
ration are frequently marked with irregular patches of 
white on all, or some, of the wings (they are “piebald” so 
to speak), and this may well result from the crossing of 
the type form with its aberration, for, occasionally, the 
hindwings are of the typical, and the forewings of the 
same specimen of the melanic, form. This “ “piebald id 
condition is very marked in some of the hybrids classed 
as delamerensis, and this increased “piebald” condition 
may be the result of hybridity, although one hesitates to 
say it is so. The ground-colour of the ab. delamerensis 
so-called, which occurs among the hybrids, is of a much 
more uniform grey (especially in the females), the scales 
ill-developed, the markings weak or obsolete, and the size 
small, in almost all individuals that emerged quickly as a 
second brood. These features are undoubtedly referable 
to the hybridisation which has brought about rapid ma- 
turity, the hybrid larvae feeding up rapidly as do those of 
T. bistortata, producmg a second brood, a phenomenon 
practically unknown in nature in 7’. crepuscularia. It 
may, therefore, be looked upon as the influence of 7. 
bistortata on the hybrids, since the second brood of this 
species is characterised by small size, ill-developed mark- 
