THE BRITISH NATURALIST. 



67 



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 

 Leucanidce are not the only fen frequenting Lepidoptera in which these 

 pale colours predominate. Macrogaster arundinis, Lcelia ccenosa, Lithosia 

 muscerda may be cited among Bombyces, and they are of very different 

 habits; Collix sparsata, 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 humidit} T , coupled with an area in which large 

 quantities of smoke are being produced, e.g. Leucania impura and L. pallens 

 produce much darker specimens in the London marshes, than in the 

 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 phis smoke which is supposed to make these 

 darker in the London marshes than in the open 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 



