Hybridising T. bistortata and T. crepuscularia. 41 
that form is the younger phylogenetically and therefore 
less prepotent), suggests very strongly that the insects 
under consideration are true and distinct species. It also 
shows that if, accidental hybridisation took place in 
nature, the progeny of the hybrids thus produced would, 
if such hybrids paired with either parent species, lose its 
separate identity and merge at once into that parent 
species with which it crossed. Although possible, it 
appears very improbable that any lepidopterous hybrids 
would in nature continue their race apart, and this, not 
from any want of vigour, but from want of sufficient 
isolation. Given the latter, then it is quite possible 
that they should do so. It must not be overlooked that 
the continuous-brooded element introduced into their 
habits would also tend to their destruction, as the eggs 
laid during October and November would hatch and the 
larvee perish from want of food. 
The tendency for all the late-emerging specimens to be 
entirely different from either (1) the Clevedon spring form 
of 7. bistortata (=ab. abietaria, Haw.), (2) the Clevedon 
summer form of 7’. bistortata (= ab. consonaria, St.), (3) the 
typical Yorkshire form of 7’. crepuscularia, or (4) the T. 
ab. delamerensis, and to develop a form identical with the 
Perthshire 7. bistortata, a form that does not occur in 
England, but which closely resembles that found on the 
Continent, in certain Asiatic portions of the Palearctic 
region, and in the Nearctic region, suggests most strongly 
that the Perth form is, so far as the forms occurring in 
Britain are concerned, the natural type form of the species. 
This vast distribution of 7. bistortata, when compared 
with the restricted range of 7. crepuscularia (so far as it 
is known), strongly supports the view that 7’. bistortata 
is the older species phylogenetically. 
As bearing out No. 12 of my conclusions, Dr. Riding 
remarks: “The fact of all the insects taking after Tephrosia 
bistortata in habits, 2.¢., in a second and even third (second 
generation of hybrids) emergence in the same year, is 
remarkable. Virtually, none takes after 7. crepuscularia 
and 7’. ab. delamerensis in this respect. The environment 
and captivity cannot have anything to do with causation, 
as I have pupe of both these latter and of Perth 7. 
bistortata—bred more or less about the same time and under 
the same conditions—all going over the winter as pup.” 
Dr Riding further adds: “It may be well to note the 
