NOTES ON THE GENUS LYC.ENA. 125 



distributed over a wide area, and in the various new localities 

 occupied would have to compete for existence with other animals 

 already established therein. The survival and increase or 

 deterioration and extinction of a form in any situation would 

 depend upon the ability of such form to adapt itself to its 

 surroundings, and here " natural selection " would exert a 

 controlling influence; but this influence would operate prin- 

 cipally in perpetuating, the most suitable colour and style of 

 ornamentation on the under surface of the wintjs.* 



The most ubiquitous species in the group is undoubtedly 

 icarus. This is the dominant form, and from the fact of its 

 occurring in high latitudes at the present day we may infer that 

 it was among the earliest to migrate northwards. The first 

 portions of Great Britain inhabited by icarus were probably 

 Scotland and its islands, from whence it extended into Ireland. 

 The progenitors of Scotch and Irish icarus would have come 

 through North-west Europe, — at tlie time our islands formed 

 part of the continent, — and were presumably of a more robust 

 character than the individuals which subsequently came into 

 England through France. The species would appear to have 

 possessed a wonderful power of adapting itself to circumstances, 

 as it is found to be established in all kinds of situations, and in a 

 variety of climates. In the course of its migrations, icarus would 

 found colonies on mountain and in valley, and some of these 

 colonies would, as time went on, become isolated. Any aberration 

 obtaining largely among the individuals so isolated would become 

 specialised, and a new form developed. Many such forms have 

 probably existed, but are now extinct ; others are exceedingly 

 local, and so greatly modified that their origin is unsuspected; 

 whilst another, hylas to wit, although apparently independent of 



* In whatever way a particular shade of blue was acquired by the males, sexual 

 selection, acting through the choice of the female, would determine the continuance 

 or suppression of such colour. Natural selection would regulate the adornment of 

 the under side of both sexes ; so that altliough a male might have the upper surface 

 coloured as in cros var. eroides, for instance, the reproduction of this colour in the 

 descendants of such male would not necessarily involve any change in the under- 

 side colour or marking, so long as those characters were in harmony with the 

 insect's surroundings. On the other hand, some variation in one or other of the 

 iinder-side characters of an insect, say icarus var. icarinus, might confer certain 

 advantages in a particular locality, and such modification would assuredly be 

 repeated in the descendants of that insect, but without any concurrent change in the 

 colour of upper surface. 



