56 LEPIDOPTEROUS FAUNA OF PORTLAND. 



vol. of " Proceedings "), which tends to become very pale in colour 

 in some localities on the South coast. I exhibit a drawing of this 

 pale var. ingratella, and also one of a pale variety, taken at 

 Portland by the Rev. 0. P. Cambridge, which does not, however, 

 at all resemble the usual pale form ingratella (Proc. D. N. H. and 

 A. F. C., vol. x., plate 13, p. 197, figs. 9, 10). Strange to say, though 

 this species is extremely common at Portland, I have never seen 

 there any of the very light varieties. My experience is that those 

 taken there are, as a rule, very constant in shade, and only a little, 

 if at all, lighter than the ordinary inland form. This fact, and 

 also the fact that there are much whiter rocks in many other places 

 where S. mercurella occurs and no var. Portlandica, would tend to 

 throw doubt on its connection with the whitish rocks of Portland. 

 But we know so very little of the laws of variation and its 

 connection with the form or colour of external objects that, though 

 we can invent theories to account for the facts which we observe, 

 such as the white colour of this variety, it is different when we 

 come to take what appears to be a similar case, as of S. dubitalis, 

 and apply to it the same theory, for, as in this particular instance, 

 we often find that it is impossible to deduce results in accordance 

 with our facts. What seem to us the merest trifles are often 

 matters of life and death to insects, and I think that there can be 

 no doubt that they are greatly influenced in their variation by 

 causes to which, if we thought of them at all, we should not attach 

 the slightest importance, and that this is the reason why it is so 

 hard to lay down any laws of variation for moths. In var. 

 Portlandica perhaps the effect of the white rocks is predominant, 

 and a white variety results; in S. dubitalis other causes may 

 produce the light variety in other places, and, perhaps, the fact of 

 its possessing ochreous and grey markings on a whitish ground may 

 protect it at Portland, as well as, or better than, if it were more 

 white. If this is the case the cause which is present in var. 

 rrf!andica would not exist in S. dubitalis. An interesting 

 question in connection with this variety is as to the reason why 

 the dark form is found at all in Portland, as well as the var. 



