40 Mr. J. W. Tutt on recent Hxpervments in 
pair and in turn produce progeny, and so on ad. wf. 
Even the TZ. crepuscularia, one of the most regularly 
single-brooded species in England (only five undoubted 
second-brood specimens are known) are unable to prevent 
this. Broods of almost all the crosses are now feeding, 
and in one case, at least, larvee of hybrids of the third 
generation. Allowance must of course be made for the 
tendency of the prepotent 7. bistortata to be double- 
brooded (and that it will occasionally also produce an 
individual or so of a third brood), but these broods emerge 
almost entirely and appear capable of going on indefinitely 
if food be provided. The same tendency is observable in 
hybrid Smerinthus populi-ocellatus, both parents of which 
are normally single-brooded species, but the hybrids from 
which always emerge in autumn as a second brood (vide 
Ent. Record, I, pp. 202-203, where Kirk gives :—Pairing 
May 31st, 1890; larve pupated July 20-27th; ten 
imagines bred after being in pupa three weeks; normal 
S. ocellatus and S. populi fed up side by side going over 
the winter). It is also observable in hybrid Amphidasys 
strataria-betularia, both of which parents are absolutely 
single-brooded (vide Ent. Record, II, p. 88, where Dr. 
Chapman records a ¢ A. stratarwa paired with a Q A. 
betularia ab. doubledayaria; fertile eggs produced ; larve 
fed up on sallow and oak ; half-a-dozen larvee missed a 
moult and pupated early; emerged some time during 
winter (as they were found dead in spring).| 
The following general observations have also been noted _ 
in my examination of the insects :— 
The influence of the male parent is less than that of 
the female, as shown by the percentages of Z. ab. 
delamerensis, but this varies with individual broods. 
When 7’. bistortata is the male parent, the progeny 
is more vigorous than when 7’. crepuscularia is the male 
parent. 
The greater vigour of the male results largely in the 
production of female offspring. When the male is of the 
dominant species, females are developed in fair propor- 
tion; when the female is of the predominant species, 
males are largely in excess. 
The hybrid facies of all the first crosses, and the ease 
(judged from the one large brood at disposal) with which 
the progeny of first crosses revert to one or other of 
the parent forms, when crossed therewith (even when 
