VAEIATION. 199 



There is considerable material for reflection in Mr. Grote's note to 

 which off-hand suggestions wovild not be wise, but, to his paragraph 

 relating to " whether dark and wet localities produce melanitic 

 individuals belonging to species which in other places never produce 

 black examjjles," or whether " we are jvistified in holding that wet and 

 dark places only act upon species having a latent tendency to melanism," 

 I would offer a few suggestions, although I have previously dealt more 

 or less directly with tlie facts involved. That only an approximate 

 attempt can be made to answer these questions is evident, for how are 

 we to determine what species have a latent tendency to melanism until 

 some unusual factor draws such latent tendency out and makes it 

 visible to us ? As an example of what I mean, our GnopJios obscurata on 

 the Sussex chalk hills, are white or whitish-grey, and a series of some 

 dozens from this locality would never give us a hint that there was in 

 the species a latent tendency to melanism, and the race in this locality 

 is a very constant one. At Folkestone, although a very large percentage 

 are of the pale type, banded forms are not infrequent, and dark grey 

 specimens are by no means rare. Here the inherent tendency is made 

 manifest by general variation. In the New Forest and in the neighbour- 

 hood of Perth, no pale siDecimens are to be obtained.; all are black. 

 The action of " natural selection " in the localities frequented by the 

 species in the latter places, is self-evident, and is evidently dependent 

 on the habits of the insect, and the dark (natural) coloration of the 

 geological strata on which they are found. In a similar way, the buff 

 specimens of Tephrosia crejmscularia, which abound in our Kent woods, 

 give us no clue as to the inherent tendency to melanism as exhibited in 

 the species in South Wales, nor do the pale specimens of T. bmnclularia, 

 in our south-east counties suggest the melanic tendency in the species 

 which is developed in Derby, Mansiield, Yorkshire, Staffordshire, &c. 

 But although a straightforward answer is in this way almost imjDOSsible, 

 I take it that such places would act upon species (which we are not 

 aware have a melanic tendency) and produce general variation, and 

 that when such general variation had been once set up, then, if me- 

 lanism were an advantageous form, " natural selection " would preserve 

 it in direct proportion to its advantage to the species. It is too 

 complex a subject, however, to be handled in a short explanatory note 

 of this kind, but there can be no doubt that items of this kind must be 

 worked out by us, or by those who follow us. — J. W. Tutt. June, 

 1893. 



ARIATION. 



Variation of the larv^ of Saturnia carpini. — In June, 1892, I 

 took a brood of young larva3 of this species on a whitethorn hedge near 

 Thundersley, in Essex. From a <? and $ , reared from these larvae, I 

 got a batch of ova this spring ; these hatched in about twenty days. 

 After their first moult, the larvfe varied very widely, some of them 

 being entirely gi'een or pale yellow, without any black, some remaining 

 (until their third moult) quite black, with the exception of a reddish or 

 brownish stripe along the side. The latter retained a large proportion of 

 black in their coloration until nearly full-fed, while others, exhibiting 

 nearly every grade between these two extremes, could be picked out of 



