6 
THE ENTOMOLOGIST S RECORD. 
present known, point, I think, somewhat forcibly to this con- 
clusion ” {Trans. Ent. Soc. Loud., 1890, pp. liv., Iv.). 
These remarks suggest many ideas, and open up new stand- 
points from which the subject may be discussed, and the 
following suggestions at once presented themselves to me as I 
heard the address. 
Although I certainly look on moisture rather as an indirect 
than a direct cause of melanism, I am not inclined to discount 
the probability of ‘‘ 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.” To a great extent our knowledge of 
the fauna of these districts is more or less confined to the 
larger and more conspicuous of the lepidoptera, especially 
diurnal lepidoptera, whose habits would render them less 
susceptible to these influences, their environment leading them 
to vary mainly in other directions. When the nocturnal lepi- 
dopterous fauna of these districts is as intimately known as our 
own, I feel satisfied that numerous cases of melanism will come 
to light proving that the combined influence (direct and in- 
direct) of moisture and “ natural selection ” are of general 
application. 
Lord Walsingham’s idea as to the action of the actinic rays 
of the sun in producing colour, and the absorption of certain 
of these rays by clouds, etc., as a probable cause of melanism, 
is quite new to me, and has proved of great interest, although 
at present I cannot see my way clearly to accept the sugges- 
tions to which the idea leads. I suppose that since the solar 
spectrum consists of heat, luminous and actinic rays, we may 
perhaps assume that a lessened amount of luminous rays, after 
having filtered through 'clouds, etc., is accompanied by a 
fewer number of actinic rays, and that the clouds may have a 
corresponding absorptive and diffusive ^ power over these rays as 
they have over the luminous. Considering, too, the well-known 
phenomenon of the decomposition of carbon dioxide by the 
chlorophyll of plants in the presence of water, by the direct 
action of the actinic rays, there seems a superficial reason for 
considering that these rays may have, as is observed by Lord 
Walsingham, some action on the chlorophyll in the pigment of 
^ The absorptive and dispersive power of aqueous vapour on the ultra-red (or heat) 
rays of the spectrum is well known : see Ganot’s Physics, par. 959. It becomes 
certain, therefore, that the influence of vapour is to increase the quantity of obscure 
(ultra-red or heat) rays, and to lessen the luminous and ultra-violet (or actinic) rays, 
in proportion to the increase in the ultra-red. 
