Variety 1 3 1 



wards — to the Clyde in the west and to Aberdeen in 

 the east — the southern English form is altogether 

 absent, and all the specimens of the butterfly to be 

 found show in an intensified degree the variation 

 characteristic of northern England. The central spot 

 above the forewings is pure white without a trace of 

 black, while the marginal orange spots have almost 

 vanished in the males and are much reduced in the 

 females. The spots beneath the wings are all pure 

 white ; only occasionally do some of them show a 

 central black speck (fig. 82 c, d). 



These typical Scotch insects differ so markedly 

 from those found in the south of England that they 

 were formerly believed to belong to a distinct kind. 

 This opinion received confirmation in the fact that 

 while the southern form has two life-cycles in the 

 year (the June butterflies laying eggs which develop 

 into a fresh generation of butterflies in August, the 

 offspring of these surviving the winter as caterpillars) ; 

 the northern form has but a single brood (the butter- 

 flies appearing in June and July, and the caterpillars 

 hatched from their eggs not pupating until the follow- 

 ing spring). But the study of the insect in the north 

 of England (especially in Durham) has shown, as we 

 have seen, that both the Scotch and southern forms 

 occur together, and that every intermediate link be- 

 tween them can be found. Moreover, all these diverse 

 forms can be reared from the same batch of eggs. 

 No doubt remains therefore that the Scotch and 

 southern insects are not distinct kinds, but varieties of 

 one kind. And instead of writing the name of the 

 Scotch insect as formerly, Polyommaius artaxerxes, we 

 write Polyommatus astrarche var. artaxerxes, the term 

 variety being applied where one form differs from 

 another to a recognisable extent, while, nevertheless, 

 intermediate forms are known to bridge over the gap 



