TEPHROSIA CREPUSCULARIA AND T. BIUNDULARIA. Pari A 
a point somewhat unduly to argue that this Wiltshire example is 
distinct from the North Devon specimens because it has a slightly 
different colour, and was taken a few weeks earlier. But suppose 
we admit that it is distinct, then what are we to say about certain 
other examples in the Wiltshire group, which are as like Essex 
June specimens as this insect from widely distant localities can 
be? The question of earlier or later emergence apart,—if the 
Wiltshire insects are crepuscularia, so also are those from 
Essex; or if the specimens from Essex are biundularia, then so 
also are those from Wiltshire. This is tantamount to saying that 
the insects from both localities are of the same species, and as 
such I certainly regard them. 
The fact of an insect appearing in the perfect state at three 
distinct periods of the year is exceptional only in one respect,— 
that is, the first and third flights of crepuscularia would appear to be 
quite independent of the second or middle brood. I am of opinion 
that the first of these broods cannot be other than an earlier 
emergence, influenced by climate in the first instance and 
perpetuated by inheritance; the third brood, which by the way 
is only partial, is a natural sequel to precocious emergence; the 
imagines of the intermediate brood are the stock from which the 
earlier form has been developed. These last still retain, as regards 
the time of emergence, the original habits of the species. Con- 
sidered in this light, the occurrence of double- and single-brooded 
forms of a species in one and the same locality is not so incom- 
prehensible as at first it would seem to be, especially if we at the 
same time have regard to the probable origin of this species.’ 
All the European species of the genus Tephrosia in the larval 
state are partial to birch, alder, and fir; this is more especially 
so with crepuscularia and punctulata. As we now find these two 
species have attained a higher latitude than their congeners, we 
may suppose that they were the forms best fitted to push forwards 
at the time when, after the ice age, animals and piants were 
returning northwards from Central and South Europe. 
Crepuscularia, as it followed the receding cold, would seize on 
every favourable locality and establish itself therein. In course 
of time, as the climate became warmer, first a portion, then the 
whole, of the imagines would be induced to emerge at an earlier 
period of the year, and the larvee would take to other food than 
that afforded by the Betulacee and Conifer. Then the early 
