Hybridising T. bistortata and T. crepuscularia, 39 
quite unlike anything ever obtained in nature. [This is 
very evident in Dr. Riding’s double brood of ¢ hybr. 
delamerensis-bistortata x & hybr. bistortata-delamerensis. I 
consider this and Mr. Bacot’s inbred hybrids in many ways 
the most important crosses of all, for they prove absolutely 
that the species operated on are really distinct. If, as has 
been stated, these were simply two racial forms of the 
same species, with independent life-histories, existing side 
by side in the same districts, these crosses should have pro- 
duced one or other of the parent form (or the parent form if 
both are identical). The production of forms quite 
unknown in nature by crossing would be quite inexplicable 
if the species were in any way identical. These experi- 
ments support Eimer’s view that sexual combination can 
lead to the production of new forms. I doubt, however, 
very much whether they could be perpetuated without 
selection, and should such a cross occur in nature, it 
would in my opinion (ante, p. 38, par. 8) revert at once if 
crossed with one of the parent species, and isolation and 
selection would both have to be carried out for the per- 
petuation of the new form.] 
11. The darkest, best-marked, largest and most 
vigorous specimens are those which remain longest in 
the pupal state. [The fact of the females being normally 
paler than the males in both parent species, suggests that 
they have less energy (and material) at disposal for 
pigment-formation than have the males, more energy 
being required for the formation of the ova. When 
small and of a very pale form, the females are the first to 
emerge (see Riding, Batch IT.), the males following on 
quickly ; on the other hand, when they are larger, darker, 
and more vigorous, they emerge after the males (vide 
Bacot, Batch VIIL). Asa rule, it may be taken that the 
size, vigour, and depth of colour are almost directly 
proportional to the length of pupal life. The gradation in 
colour (apart from ab. delamerensis) in some of the broods 
is most remarkable. The very late emerging specimens in 
Dr. Riding’s Batches III. and IV., have resulted in the 
production of specimens quite different in hue from the 
colours reached by the parent species, either at Clevedon 
or York.] 
12. The hybrids have lost all regularity as to the time 
of emergence, 7.¢., hybridity causes continuous-brooded- 
ness. [All the crosses result in producing progeny which 
