44 
a distinct idea of what I consider one potent and active force, I dis¬ 
cussed the action of moisture at length, because it is that force which 
most intimately concerns British lepidopterists. At the same time, I 
went into other side views that Nature takes—temperature, heredity, 
environment, natural selection, etc.—partly to show that I knew such 
existed, but more particularly because it is impossible to discuss one 
view without considering others. These are the symptoms of mental 
aberration, I suppose, to which Mr. Robson casually refers on every 
other page. 
Mr. Robson quotes Dr. Chapman as saying that he considered 
melanism to be “ a western rather than a northern form of variation ; 
to be associated with wet weather rather than a cold climate; and it 
has certainly been most common of recent years, which may be 
attributed to the long succession (unprecedented) of wet seasons we 
have passed through,” and yet goes on to conclude (from this, I pre¬ 
sume) that “ Dr. Chapman, who is one of the most thoughtful and 
original of all students of Lepidoptera, does not support the idea that 
moisture produces melanism.” Truly, these depths are beyond me. 
The quotation Mr. Robson gives appears to be a sufficient refutation of 
his own conclusion. Mr. Robson clearly does not discriminate between 
the two effects of moisture, the effect “ that selects varieties ” and 
the effect “ that makes them.” So far as we have been able to get at 
the latter, Dr. Chapman’s notes ( Melanism and Melanochroism in British 
Lepidoptera, pp. 60-64) are lucid enough. Mr. Robson seems to have 
overlooked them, or not to have noticed that they deal with the matter. 
Some of the odds and ends of Mr. Robson’s paper are most startling. 
Mr. Robson’s want of knowledge of the rainfall of our Fen districts, of 
the,response to environment of our Fen species, of the influence of the 
Gulf Stream on the meteorology of the British Isles generally, and of 
certain parts in particular, leads one to suggest that there are still a few 
books on meteorology and physical geography to be obtained in some of 
the various libraries scattered over the country. He also states, too, 
that “ these melanic forms did not exist half a century ago.” What 
melanic forms ? I would ask. The melanic forms of Gnophos obscurata 
on the peat bogs of the New Forest or on the dark rocks of Perth; the 
black Xylophasia polyodon of the Irish coast, Scotland, etc.; the black 
Agrotis lucernea of the Kincardineshire and the Irish coasts; the dark 
barrettii form of Dianthoecia luteago or the manani form of D. ccesia ; the 
dark Scotch forms of Larentia ccesiata, or the black moorland forms of 
Hypsipetes elutata; the Scotch plumbata form of Melanthia rubiginata , 
the dark Wicken form of Acidalia bisetata, or the Dartmoor form of 
A. marginepunctata; the Wicken black var. of Chilo phragmitellus, and 
endless others ? If he say so, I am certain he stands alone, and the 
statement would be laughed at by every scientific lepidopterist in the 
country. On the other hand, if he refers to Amphidasys betularia var. 
doubleday aria, to Polia chi var. suffusa, to Cuspidia psi var. suffusa, or 
Eupithecia rectangulata var. nigrosericeata, I should be inclined to agree 
with him, as the present conditions of environment were so different 
then from what they are now; but ages before that, when the physical 
geography of England was somewhat different from what it is now, 
and large forests were the rule, dark forms probably existed, and the 
species have simply reverted by a series of changed conditions in their 
environment in recent years. 
