150 The Classification of Insects 



Polyommatiis, is the same for both species. It is the 

 generic name, and indicates that the two butterflies are 

 so closely related to each other that they are classed 

 by naturalists in the same Genus, a genus being an 

 assemblage of species which possess so many characters 

 in common as to suggest that they have not diverged 

 very widely from their common stock. The genus 

 Polyommatus takes its name from the numerous eye- 

 spots on the under side of the wings of the butterflies 

 included in it. These, together with the marginal 

 orange spots beneath the hindwings, are the most 

 characteristic markings of the group. In the vast 

 majority of the species, as in P. icarus, the upper 

 surface of the wings is some shade of blue in the 

 male, brown with blue dusting in the female. 



There is another blue butterfly found in our islands 

 which frequents woods and thickets rather than the 

 open hillside where one finds the species of Polyom- 

 matus so abundantly. The upper surface of the 

 wings in both sexes is lilac blue, the female being 

 distinguished by a black border along the termen of 

 the forewing. Beneath, the wings are very pale 

 blue, each with a central half-moon-shaped black spot, 

 between which and the termen comes a row of small 

 circular black spots ; the hindwing has in addition a 

 few black basal spots. None of the spots are "eyed," 

 nor are there any orange spots at all. This insect, 

 whose specific name is argiolus, is the only British 

 butterfly which exhibits such markings beneath the 

 wings, but many similar species are known in other 

 parts of the world. Its typical markings differ so 

 from those of Polyommatus that most students of 

 butterflies regard it as belonging to a separate genus, 

 Cyaniris, and call it therefore Cyaniris argiolus. 



But just as the terms "variety" and "species" are 

 incapable of strict definition and depend largely on 



