Vll. 
open fields near Strood in Kent, and Scotch specimens are occasion¬ 
ally darker still. Again, Agrotis nigricans is blacker from the Greenwich 
marshes than from the fields and marshes in the neighbourhood 
of Rochester. But Leucania impura and pallens have no right to be 
called “ Marsh-frequenting species.” They abound in dry places like 
our sand-hills at Hartlepool, and are so generally abundant that it is 
only in exceptional localities that they do not occur. But we must 
notice that it is humidity plus smoke which is supposed to make these 
darker in the London marshes than in the ooen fields of Kent, and 
does it not seem as if smoke had more to do with it than humidity, 
when he tells us in the next sentence, that Agrotis nigricans is darker 
in the marshes at Greenwich than in those near Rochester. As for 
this insect, I have taken it on our dry sand-hills at Hartlepool, quite 
as dark as the darkest in Mr. Tutt's lengthy series, and what is more, 
we never by any chance take a light coloured one. 
With reference to this assumed change of view, it must be 
remembered that the earlier portion had been written a year or two 
before, and that as it had appeared, the question was being discussed 
in his correspondence, and he was extending his remarks and enlarging 
his views in consequence. But the clear and definite theory, that 
melanism was the result of the westerly winds charged with moisture 
from the Gulf Stream, is no longer put forward as the active agent it 
was assumed to be at first, but moisture is now spoken of as an 
indirect or secondary cause at most. Thus at p. 48 he refers again 
to swamp}- climates, and says : “ But if moisture is to be taken as a 
direct, rather than an indirect cause, we should expect to find melanic 
variation occurring in the swamps of Tropical Africa, in the Forests 
of the Amazon, on the banks of the Mississippi, and in many other damp 
climates, even within tropical regions, and I am not aware that this is 
the case.” And on the next page “ Although I certainly look on 
moisture as an indirect rather than a direct cause of melanism.” 
Still further to emphasize the point I wish to make, that the settled 
opinions of the earlier pages, were settled no longer, he writes on p. 49 
“ Lord Walsingham’s idea as to the action of the actinic rays of the 
sun in producing colour, and the absorbtion of certain of these rays 
by clouds, &c., as a probable cause of melanism, is quite new to me,” 
and after discussing this point, he says (p. 50) : “ Although I thus still 
venture to differ from Lord Walsingham, I must candidly confess 
that his remarks have modified my previously formed opinions, and 
that I should not now feel inclined to give the probable action of 
sunlight such short shrift as I gave it in a previous paragraph.” 
But though we find in this portion of the pamphlet an inclination to 
retreat from the very decided views enunciated at the beginning, he 
returns very much to his earlier opinion before he concludes. Letters 
