IN THE BRITISH ISLANDS. 133 



they are not particularly apparent with either. The groups into which 

 the species naturally fall are : (1). Munda, instabilis, opima, gracilis* 

 (2). Populeti,gothica* stabilis, cruda. (3). Mimosa. There is probably, 

 no genus except the tritici-cursoria group of Agrotis, where the allied 

 species show such a close parallelism in variation. The close alliance 

 existing between certain species, at once suggests that such variation 

 should be expected, for, as I have before stated, " if a slight modifica- 

 tion and gradual development, owing to environment &c., bring about 

 specific distinction, it follows, that reversion and ' natural selection ' 

 generally, will, under similar conditions, aid in the development of 

 similar forms " (' Entom. Eecord ' &c., vol. i., p. 217). This parallelism 

 of variation is exhibited, not only in the coloration, but also in the 

 size, position and shape of the stigmata, in the modification of 

 the transverse, basal, elbowed and subterminal lines, and also in 

 the central transverse shade, as well as in the development of the 

 transverse row of dots or wedge-shaped marks parallel to the hind 

 margin. In all the species, the characters which are normal in 

 one are almost sure to be developed abnormally in the allied 

 species, and vice versa. With regard to this parallel variation, Dr. 

 Chapman writes : " You find, I have no doubt, among the species of 

 T&niocampa, what is true more or less in most genera, viz. : that each 

 species varies in the direction of other species of the genus. Thus 

 munda has a suffused (cruda) form. Stabilis has a form with a dark 

 central shade (instabilis). Cruda has a rosy form (miniosa), a dotted 

 form (munda), a form with well-marked stigmata (stabilis), &G. Popu- 

 leti, opima and instabilis have a form with dots on the subterminal line 

 (munda), and so on. I suppose one might work at them, till vars. of 

 each species were obtained which represented each of the others " 

 (in litt.). Tceniocampa instabilis is perhaps the most variable species 

 of the genus, if indeed it be possible to select one as " most variable," 

 where all vary so excessively. With a ground colour extending from 

 a pale whitish-grey to the brightest red and most intense black, with 

 a transverse shade extending sometimes as a broad black band, whilst 

 at others it is quite obsolete, and with the transverse lines exhibiting 

 almost every possible phase of development, it perhaps really deserves 

 the term " most variable." But gracilis and opima have equally pale 

 and equally dark varieties, the former also equally red ones, whilst 

 populeti has a most intense black form. Stabilis is sometimes of the 

 palest grey, at others much suffused, whilst some are of the brightest 

 red coloration. T. pulverulenta (cruda) and miniosa, perhaps, vary least, 

 but still they do vary, and that considerably within narrow limits. 

 The effect of environment on species is well exhibited in instabilis. 

 The specimens from Hereford are of all forms, the pale ones, however, 

 tending to reddish, but the dark ones very black. The dark ones are 

 equally black in Kent, but the pale ones generally tend to grey, whilst, 

 in Forres, the pale ones are apparently nearly all reddish-tinted, and 

 dark forms are comparatively rare. This statement is based on the 

 material at my disposal, and may have to be modified when more is 

 known of the species in different localities, but at present more than 

 50 per cent of all the specimens I have received have been dark, 



* These are transposed at Entom. Record' Ac., vol. i., p. 217. 



