MELANISM IN LEPIDOPTERA. 33 



of these dark varieties, I was somewhat surprised to see what may be 

 called the " birthmark " theory revived to account for them by Mr. 

 Fetherstonhaugh (p. 215), and subsequently supported by Mr. Tugwell 

 (p. 256). It is almost impossible to one having any physiological know- 

 ledge to see how any impression on the sensorium of the parent can 

 produce any permanent change (except, perhaps, a deficiency in some 

 parts) in the structure of its offspring. As, however, one fact is worth 

 a hundred theories, I may perhaps be allowed to quote here a passage 

 from Darwin's 'Animals and Plants under Domestication* (1st edit, 

 vol. ii. p. 263), which seems to me to be decidedly " ad rem " as regards 

 the subject under discussion. He says, " it was formerly a common be- 

 lief, still held by some persons, that the imagination of the mother affects 



the child in the womb Dr. William Hunter, in the last century, 



told my father that during many years every woman in a large London 

 lying-in hospital was asked before her confinement, whether anything had 

 specially affected her mind, and the answer was written down ; and it so 

 happened that in no one instance could a coincidence be detected between 

 the woman's answer and any abnormal structure ; -but when she knew the 

 nature of the structure, she frequently suggested some fresh cause ! " 

 Natural selection perfectly explains the facts adduced by Mr. Tugwell 

 about Gnophus obscuraria, for of course on a dark soil the darker indivi- 

 duals, on the light the lighter ones, will be best protected by their colours 

 and will therefore have a better chance of escaping the notice of their 

 enemies. That the dark colour of the soil can hardly be the true cause 

 in producing these variations is, I think, pretty certain, from their occur- 

 rence in many places where the soil is not conspicuously dark, e. y. the 

 Highlands of Scotland and the Alps *. I have just been looking through 

 Dr. Staudinger's catalogue, and was much struck by the fact that in 

 nearly every case where a local form (whether a " var. " or " ab. ") from 

 the Alps is noticed, it is characterized as being " obscurior " or " multo 

 obscurior," or with some of the markings " obsoleta." The great number 

 of normally dark or black species of Lepidoptera in the Alps, as, for 

 instance, the Erebice, Psodos, and some Pyralides (cf. Jordon, vol. xiii. 

 p. 60), seems to me also to be worth notice in connection with this subject. 

 In a few cases, Alpine insects are only sexually melanic, e. g. Pieris napi 

 $ , var. bryonice, A. paphia $ , var. valezina, Polyommatus virgaurece $ t 

 var. zermattensls. These cases are explicable on the theory that sup- 

 posing sexual selection to have been such an efficient agent in modifying 

 species as Mr. Darwin believes, it may have been more important for the 

 males in the struggle for life to preserve their good looks than to have 

 acquired sounder constitutions at the expense of the former. That the 



* Conversely, too, one would expect, if this theory were true, to find more melanic 

 vars. on tbe very dark soil of peat-mosses and fen-lands than is actually the case. 



D 



