VI. 
Stream, and attempts to show that these are the districts where 
melanism most prevails. 
But if moisture or humidity be the cause of melanism, it would 
be reasonable to expect a preponderance of melanic forms in all 
places where moisture exists in excess. In our fens and bogs, our 
wet moors and mosses we would surely find some evidence in support 
of this theory if it were true. One of Mr. Tutt’s correspondents 
apparently made this suggestion to him after the first portions of the 
paper had appeared, for he says (p. 21) : “I have heard it suggested 
against this theory, that the insects from the marshes and similar 
situations are pale coloured, and, as instances, the Leucanidce have 
been given, on the assumption, I presume, that all insects from such 
localities should be dark ; but this does not appear to me to militate 
against the theory. I, fortunately, have been able to study the actual 
habits of the species of this family in a state of nature, and, as they 
sit head downwards, with their wings folded closely to the edges of 
the reeds on which they usually rest, the appearance they have, so 
closely resembles the nodes on a reed culm, that it is barely possible 
for a trained eye to detect them, and we may be certain that the 
peculiar colour which is so advantageous in enabling them to escape 
their enemies and thus perpetuate their species, is as directly 
dependent on “ Natural Selection ” as is the darker assimilating 
colour of those species which rest on the ground, fences, or other 
dark objects.” 
But Mr. Tutt argues here from a special case, and assumes when 
he has replied to that, that the reply has a general application. The 
Leuccmidce are not the only fen frequenting Lepidoptera in which these 
pale colours predominate. Macrogaster arundinis , Lcelia ccenosa, Litkosia 
muscerda may be cited among Bombyces, and they are of very different 
habits; Collix spavsata , the genus Chilo and many others maybe named, 
all of these ochreous tints, which certainly is the prevailing hue in the 
species that inhabit our swamps and morasses. Even our solitary 
marsh butterfly Ccenonympha davus is nearly of the same hue. But more 
than that may be said, Odonestis potatoria is paler at Wicken than in any 
other locality than I am acquainted with, and a variety of the male 
occurs there occasionally, as pale as the female. But it appears to me 
that at this stage Mr. Tutt had either abandoned, or lost the thread, 
of his argument, and that his opinion was changing, consciously, or 
more probably unconsciously, and he now imports another factor. 
He says (p. 22) : “But with regard to the pale marsh frequenting 
genera, I have specimens that prove distinctly that even these species 
vary according to general humidfiy, coupled with an area in which large 
quantities of smoke are being produced, e.g. Leucania impura and L. pattern- 
produce much darker specimens in the London marshes, than in the 
