83 THE ENTOMOLOGIST. 



A similar melanic tendency in the colour of those from moun- 

 tainous districts is thus mentioned : — 



*'It is worthy of remark that where the atmospheric conditions in any 

 degree approach to those of the more northern regions, as they do on high 

 mountain ranges, at varying elevations according to the degree of latitude, 

 the same tendency to assume a darker or more suffused colouring is very 

 observable. 



" Mr. W. A. Forbes remarks, =:= ' In looking through Dr. Staudinger's 

 catalogue I was much struck by the fact that in nearly every case where 

 a local form (whether a variety or aberration) from the Alps is noticed, it is 

 characterised as being obscurior or multo-obscurior, or with some of the 

 markings ohsoleta.' He goes on to notice the number of normally black or 

 dark species in the Alps, e. g., Erehia, Psodos, and some Pyralides." 



The author then states that various theories have been 

 advanced at different times, and by dillerent authors, to account 

 for variation in animals, birds, and insects, and it has been 

 attempted to apply some of these to the phenomena which he 

 proposes to consider : — 



" I. Since Darwin drew attention to this cause, the theory of protective 

 resemblance has been most commonly made use of to account for the varied 

 coloration of insect forms. It has been proved almost to demonstration in 

 many instances, that by more or less gradually developed assimilation to 

 surrounding objects, those varieties best adapted to escape the observation 

 of natural enemies have become perpetuated. 



"II. Many instances of varied colouring have been referred to an 

 archaic origin ; that is, to the preservation of such varieties by liereditary 

 transmission from an ancestral source. 



"III. The influence of quality and quantity of food has been brought 

 forward to account for modifications of normal colouring. 



" IV. Retarded or accelerated development depending upon climatic 

 conditions acting upon insects in their larval or pupal stages has also been 

 quoted as a cause for variation. 



" V. Insular varieties have been attributed to the effects of long 

 isolation and segregation tending to establish special races. 



" VI. Atmospheric electricity has also been called into requisition to 

 account for certain changes. 



" VII. Mr. Geo. Lewis has argued f that exposure to more or less direct 

 action of the sun's rays may influence colour by acting mechanically upon 



* ' Entomologists' Monthly Magazine,' xiv. l(i. 



+ * Transactions of Euiomological Society of London,' 1882, p. 503. 



