76 



VARIATION IN EUROPEAN LEPIDOPTERA. 



Variations from recognised types may be classed either as 

 temporar}^, though recurrent ; or persistent and hereditary. In the 

 former case they are named aberrations, and are chiefly remarkable 

 as indicating a latent tendency in the type to diverge in that particular 

 direction. These occasional aberrations, although recurrent from time 

 to time, cannot rank as varieties until they interbreed with each other, 

 which is, of course, impossible when the aberration is confined to 

 one sex (as in Argynnis Paphia female ab. Valezind)^ and give rise to a 

 race inheriting their peculiar characteristics. 



But when the divergence from the type growls persistent and 

 hereditary, it becomes a variety. And to know when it ceases to be 

 a variety, and constitutes a distinct species, we must introduce a 

 physiological test. So long as it is capable of fertile union with the 

 type, and of thereby producing a fruitful progeny, it remains a varia- 

 tion, while the question of determining w^hich is the type and which 

 the variation must be left to entomological experts. Directly, how- 

 ever, such interbreeding ceases, or produces infertile ova — or sterile 

 hybrids — it has established itself as a species. 



Having thus defined in a popular manner the arbitrary abstractions 

 which we call species, aberrations, and varieties, let us run over 

 briefly some of the chief phenomena of divergence observable among 

 the order Lepidoptera generally. 



In the first place there is the simple variabiUty of size, which is 

 I think, more frequently and most strikingly observable among the 

 Rhopalocera. One chief cause of this is doubtless the stint, or 

 unsuitable nature of their food when in the larval condition. All 

 who have bred specimens know this result of accidental or experi- 

 mental neglect. Climate acts in a like way when it stunts the 

 growth and luxuriance of the food-plant, either by an ungenial cold 

 and lack of sunshine, or, in hot countries, by parching the groimd 

 and depriving the roots of moisture. We have this strikingly ex- 

 emplified in the dwarfed Alpine representatives of genera whose 

 species have different ranges of altitude. .Compare the dwarf 

 Erehias^ Aste?'ia, Goj'ge, Mnestra, Tyndarus^ and Melampus\ which 

 are confined to the higher Alpine altitudes, with their larger con- 

 geners of the lower levels : and place beside a Lycc^na of Central 

 Europe, a specimen of the same species bred on an arid hillside of 

 France, Italy, or Greece, and you will see the same effect springing 

 from opposite influences. I have met with an interesting specimen 

 of MelitcEa Artemis, whose history is as follows : — In the county of 

 Clare, in the West of Ireland, a friend of mine went to visit a locality 

 on which, he was told, a ' shower of worms ' had fallen. He assured 

 me that, on his approach, the road was black with small larvae 



Naturalist, 



