VAlilATION. Ill 



increased l)y the liigli rainfall. Probably there is no other district in 

 England -where the same conditions obtain to the same extent as in the 

 West Kiding. Noav it is a jiositive fact that as one goes out from 

 Leeds, in any direction where there is less smoke, that the percentage 

 of melanic varieties lieeomes loss, and that the farther one goes tlie 

 lower is the proportion of varieties met with. This does not obtain in 

 all species, as for example, T. Itimulnhirin, E. vminah's, etc., but even in 

 such species as these the melanic specimens from the West Hiding are 

 usually darker than those from smokeless districts. This is especially 

 noticeable in D. fagella, prol)ably liecause this insect is more susceptible 

 to clianged conditions of life* than almost any other of our English 

 moths. Going out from Leeds I have found the percentage gradually 

 decrease, until, in a wood, fifteen miles away it was the exception to 

 find a smoky variety while in Wliarfedale. A. rnmicis, so far as my 

 experience goes, is always tyiiical. The conditions of Airedale and 

 Wliarfedale in the district of Leeds are precisely similar, except that 

 there is no smoke in Wliarfedale. One cannot lielji being struck by 

 these facts, and without Avishing to give undue emphasis to this state- 

 ment, from actual study of the environment and climate on the spot, I 

 am forced to the conclusion that smoke is the chief factor in the pro- 

 duction of melanism in the West Eiding of Yorkshire." — William 

 Mansbeidge. 



Mr. Mansljridge's conclusion is that to Avliich I have already come 

 in these pages. Li Vol. i., p 56, I write, after quoting a gi'eat 

 many examples : — '' I lielieve from this (and it appears to be a fair 

 deduction), that Lancashire and Yorkshire melanism is the result 

 of the combined action of the ' smoke ' jiihis humidity, and that the 

 intensity of Yorkshire and Lancashire melanism produced by humidity 

 and smoke is intensified by ' natural selection ' and ' hereditary 

 tendency.' " Of course I use the word " produced " here in a broad sense, 

 without going deeper into the vital and more complex physiological 

 processes which must be at Avork, and accompany such change. The 

 action of " smoke " is probably more specially indirect, and only acts 

 so far, that it heli^s the rain to permanently darken objects within 

 its area of influence, and hence re-acts by " natiu'al selection," most 

 particularly on those species which rest on fences, trees, and other 

 objects thus made permanently dark b}^ its aid. The intensification of 

 the darkening is brought about by '•' natural selection," which weeds 

 out the pale-coloured examples under these conditions by their con- 

 spicuousness. A further discussion of Yorkshire and Lancashire 

 melanism is to be found Ent. Bee. Vol. i, pp. 86-87. — J. W. Tutt. 



Melanic variety of Hybernia aurantiaria. — A few weeks ago, 

 thanks to a hint from Mr. Dennis, of the South London Society, I found 

 that a dark unicolorous variety, of what had been in my cabinet under 

 the name of H. defoh'aria, was really aurantiaria. The specimen was 

 taken at light at Horsforth, near Leeds, in September, 1890. The true 

 name of the specimen was determined by a comparison of the antennae, 



* Query. Is it not rather that, being a common species, and of the pre- 

 vailing black and white (or grey) tint, which lends itself most readily to modi- 

 fication, as well as an inhabitant of the suburbs of our large towns, and hence, 

 directly, under the darkening influence of smoke, that " natural selection " is 

 able to produce such marked response to environment in this species, rather 

 than any special inherent susceptibility in the organisation of the species ? — Ed. 



