THE ELUCIDATION OF CAUSES OF VARIATION. 87 



the Alps appear almost intermediate between my pale euphorhm 

 aad Eannoch myricfe. It seems strange that Guenee should 

 have described exactly the same variety ; first as a var. of eii- 

 phorbicB, and secondly as a distinct species. Herr Hoffmann 

 writes me that the markings of montivaga from the Engadine 

 are a little less distinct than those of myricce from Eannoch, 

 otherwise the forms are identical. 



It may be advisable, before leaving the genus Acronycta, to 

 mention a statement of Guenee's (' Histoire des Insectes,' vol. v., 

 p. 47), which I have had no means of verifying from actual 

 observation. He says, " almost all the species of this genus 

 have now and again isolated individuals distinctly suffused with 

 rose colour." Perhaps some of our lepidopterists have such. If 

 so I trust they will record them. 



(To be continued.) 



THE ELUCIDATION OF CAUSES OF VARIATION. 

 By Sydney Webb. 



From time to time, in the pages of our entomological 

 magazines, various theoretical causes have been adduced by 

 correspondents, with the hope of explaining unknown recurring 

 phenomena amongst lepidopterous insectf^, popularly known as 

 varieties ; but which, as they chiefly affect individual specimens 

 rather than whole broods, should perhaps better have been 

 termed (as indeed they are by a minority) aberrations. 



It is I think pretty generally admitted that some, if not all, 

 of the suggested disposing causes are prime agents, but there 

 the matter rests. No one attempts to carry the investigation 

 further, yet no one is satisfied with the explanations given. 

 This unanimity of dissatisfaction arises from two sources. One 

 is that an undoubted change does take place, not only in 

 botanical but entomological, and in far higher orders of animal 

 life, when kept and systematically reared in confinement, which 

 is not observable in the wild condition. The other is that where 

 in a state of nature these changes Lave bfen noticed (apait from 

 single instances) they have been partial rather than general, 

 often in a limited area of a few square miles. 



