222 THE entomologist's record. 



not " a latent tendency to melanism," but before we can assume that to be 

 a fact, we must be careful to satisfy ourselves that the conditions in each 

 case are identical, that the habits, etc. are similar, and that the necessity 

 for melanic variation is equal in each case. Given that they are, and 

 that then a species persistently refuses to be melanic, then I should say 

 that such species had " no latent tendency to melanism," but Nature 

 would avenge this wrong-headedness, and under such conditions the 

 species would become extinct. Nature rarely shows any cast-iron 

 fixity like this, and it's a very good thing for the species too, and I 

 think it probable that every species, so far as it has an inherent power 

 to vary, lias also an inherent tendency to melanism. 



Major Still's reference to Polyommatus phlwas is rather striking. 

 This is one of those objectionable species which does not care to lend 

 itself to any general theory. It is ^particularly subject to temperature 

 influences, and strangely enough the brightest specimens come 

 generally from the coldest, and the duskiest specimens from the hottest 

 places. Assuming that the open moor, although higher, has a higher 

 temperature than the low-lying situations, Major Still's experience 

 coincides in general with the variation exhibited in the species in the 

 area of its distribution, from the Arctic Circle almost to the Equator. 

 The fact that this year's specimens are esiiecially dark also agi-ees with 

 the general principles of variation everywhere observed. 



The habits of Gnophos obsciirata and Acidalia marginepunctata are 

 very similar, and the same general result is observed. The habits of 

 Tephrosia himidularia are very different. The colour of the two former 

 agrees or res2:)onds to the colour of the ground on which they rest, of 

 the last to the trunks of the trees on which it rests. With these data, 

 the problem appears to be within reach of a solution agreeing with the 

 known result. 



I fail to follow the reasoning in the last two paragraphs. On the 

 moor, according to Major Still, G. obscurata and A. marginepunctata 

 " are always dark," but these are fully exposed to light, therefore, light 

 does not prevent their melanic tendencies from becoming obvious. 

 " Tephrosia biundularia," Major Still remarks, " is found in the darkest 

 situations," and " does not show any tendency towards melanism." 

 That is, G. obscurata and A. marginepunctata being exposed to light, 

 are always melanic, and T. biundnlaria shut away from light is never 

 melanic. Therefore, I fail to see how " absence of light would seem 

 to be a more powerful factor in the production of melanic forms than 

 dampness," a conclusion which Major Still strangely reaches from the 

 above facts. 



I quite appreciate the principle involved in the last jihrase, although 

 I do not agree with its verbal form. To produce melanism, I do 

 not think " both conditions must be combined." At the same time, if 

 in any place both conditions are combined, I quite understand the 

 intensifying force on the environment of such a j^lace. Melanic forms 

 of species like Agrotis lucernea, Gnophos obscurata, Boarmia rhomboidaria, 

 Diurncea fageUa, and many other species occur as distinct races in 

 localities where there is certainly no suspicion of a lack of light or 

 even of direct sunshine. Where the shutting out of light has a 

 distinct influence on the colour of the tree trunks, etc., then we liave a 

 condition, which " natural selection " would not be slow in making 



