J. W. H. Harrison 65 



conditions. These facts hold good no matter whence the stocks employed 

 are derived. 



Then, too, enormous displacements^ amounting to several months, 

 are visible in the time of emergence of these hybrid moths ; and, what 

 is still more remarkable, the acceleration displayed by the female 

 hybrids is emphatically greater than that of the male, so that instead 

 of the males appearing first the females do so, and may anticipate the 

 opposite sex by several weeks. 



Time, amongst other changes, brings mellowness, and now, tacitly, 

 without the renewal of strife, but actually determined by the facts just 

 outlined and by the process of attrition, the two have attained an im- 

 pregnable position as far as their specific rank is concerned. 



(3) Melanism in the two species. 



Each species, then, as I have said, varies along its own line, but 

 each, in spite of this, like every other species of Tephrosia and of the 

 related genus Boarmia, produces its own peculiar melanic form or 

 forms, that of T. bistortata being known as variety passetii, and being 

 readily distinguishable from the corresponding form of T. crepuscularia 

 to which the name delamerensis is customarily applied. And whenever 

 these melanic varieties have developed in stations where the species 

 overlap they have arisen independently and at widely different times ; 

 although Sir J. T. D. Llewelyn^ observed the black variety of T. bis- 

 tortata in South Wales in 1866 it was not until the early " eighties " 

 that he captured the parallel but characteristically different melanic 

 form of T. crepuscularia. Not only are these differences perceptible in 

 the time of origin but noteworthy disagreements also exist in the head- 

 quarters of the melanic forms of each. In T. bistortata melanism seems 

 to reach its greatest intensity in South Wales although I myself have 

 captured odd specimens of melanochroic tendencies in the larch woods 

 on Wilton Moor, 3^ miles from Middlesbrough. On the other hand, the 

 melanic varieties of T. crepuscularia occur with more or less regularity 

 in all of the great industrial areas between, and including, South Wales 

 and South Durham. 



At this point it is proper to note that, whilst undeniably displaying 

 some degree of fluctuating variation within their own limits, of the same 



1 Such disturbances are not unusual in hybrid Lepidoptera but generally, whenever 

 the sexes are affected unequally, except in this case, it is the male that exhibits the greater 

 displacement. 



2 Barrett, Entomologists Monthly Magazine, Vol. ^XXI. p. 199, 



Journ. of Gen. x 5 



