198 • THE entomologist's record. 



interval, between parent and progeny ; it is a matter not onlj'^ of re- 

 version, but may be one of immediate inheritance, though not invariably. 

 Beyond this, it seems that the wet and dark places, favouring the 

 production of dark specimens, may be further held to act as agents in 

 the operation of the law of " natural selection." But the matter is chiefly 

 interesting in an experimental light, and there is a wide field before us 

 to go over. I follow Mr. Tutt in his view, that in melanism, we have 

 to do with a phenomenon of reversion, and the real or supposed causes 

 which lead to its more abundant and temporary display. My idea, 

 which Mr. Tutt now corrects, was that it only seemed to be abundant 

 in certain localities, and I offered a reason for this seeming. Biit if the 

 physical conditions of the localities directly act in the direction of 

 melanism to-day, we may have also to do with an acquired character, 

 equally siisceptible of transmission. Thus melanism, so far as the facts 

 go, may be either freshly acquired, or appear by reversion. And just 

 here comes in the question, whether dark and wet localities produce 

 melanic individuals belonging to si^ecies which, in other places, never 

 produce distinctly black examples. Or are we justified in holding that 

 wet and dark places only act upon species having a latent tendency to 

 melanism ? To work out all tlie factors in the case, is a matter for our 

 patience and ingenuity, and I shall be very glad if anything in my very 

 modest and wholly tentative remarks proves of interest to students of 

 the subject, among whom, Mr. Tutt, who has already done so much, 

 occuiDies deservedly so prominent a position. At any rate, in their 

 correction, the better view will have become more plain. — Bremen, 

 Germany. 



Mr. Grote is quite right in saying that the experiments on the 

 Indian butterflies " do not entirely " cover the question of melanism, 

 but they do give us one very strong scientific fact, and that is, that 

 moisture can so unsettle as it were the normal constitution of the larva 

 that its natural hereditary tendency to produce a certain form is over- 

 come and another form is produced in its place. It further shows us 

 that moisture can act on the constitution of a larva as to produce or 

 intensify certain general forms of variation. This being so, I think it a 

 fair assumption that the excessive moisture of parts of the British Isles 

 should produce a certain amovmt of variation in certain species, and when 

 we find, as we do, that such localities do produce a gi-eat amount of 

 general variation in certain species, and when further we cannot point 

 to any other active factor which can probably produce such variation in 

 these districts, I think it a fair assumption (knowing the capabilities of 

 moisture) to suppose that the variation is thus originated in such 

 localities. The summary of Mr. Edwards' experiments in dimorphic and 

 polymorphic butterflies, as given by Mr. Grote, is sufficient to prove 

 my point, viz., that external influences, of which humidity is one, are 

 sufficient to produce variation, or as Mr. Grote puts it, produce " a ten- 

 dency to meet these conditions," as " shown in the colours and jjattern 

 of the insects." So far, I take it, " melanism " is parallel with " dimor- 

 phism," in fact, with any other form of variation, inasmuch as both 

 (or all) may require an active agent to prodvice the initial variation 

 which has to be moulded into its various forms. Having obtained this 

 initial variation, " natural selection " steps in and selects those varieties 

 which are most suitable by environment and by constitution to that 

 special locality, and a permanent (so long as the local conditions are 

 unaltered) race is formed. 



