270 



THE ENTOMOLOGIST. 



greater facilities ior establishing themselves than the entomo- 

 philous i^lant eaters. Similarly, as annual and low -growing plants 

 sooner reach maturity than perennial herbs and plants of a 

 shrubby or arboreal nature, the insects which find their food on 

 them would have a slight advantage. 



Again, on the other hand, it is not unnatural to suppose that 

 the butterflies which are now found within the arctic circle were 

 better fitted to follow closer the retreating ice-sheets and snow- 

 fields than those species which are not found outside the more 

 temperate regions. 



We will now see how these theories work with the British 

 butterflies. Of the twenty- one which are arctic, the greater 

 number feed on low plants, which are either wind-fertilised or 

 more or less adapted for self- fertilisation. Along with the arctic 

 species two others may be taken, viz., Epijjhroji and Mthiops, 

 which, though not arctic, are alpine and subalpine. Their larvae 

 live also upon anemophilous plants. Keeping in mind then the 

 food-plants, the distribution of the insects, and the nature of the 

 localities which they inhabit, we may arrange these twenty- three 

 in the following manner, indicating the order of their arrival in 

 Britain : — 



1. Typhon, Pamphilus, Epiphron, Mthiops, feeders on grasses 

 and sedges, and inhabiting moory ground, such as we may suppose 

 to have been formed early in post-glacial times. 



2. Icarus, Phlaas, Tithonus, Aglaia, Euphrosyne, Selene, 

 Lathonia, Athalia, Urticcs, Nap'i, Cardamines, also feeders on low 

 plants either wind-fertilised or chiefly adapted for self- fertilisation. 

 Many of them also inhabiting moor}^ situations. 



3. Astrarche, Machaon, Comma, jEgon, Semiargus, Ruhi, 

 Malvce, Antiopa, mostly feeding on plants where cross fertilisation 

 by insect-agency prevails, some of them being also of a shrubby 

 nature. 



The remaining species, which are not arctic, may be arranged 

 in like manner : — 



1. Semele, Megcera, Janira, Hyperanthus, Mgeria, Sylvanus, 

 TJiaumas, Palcemon, Actceon, Atalanta, lo, Cinxia, Adippe, 

 Galathea, Sinapis, Daplidice, Brassicce, all feeders on low plants 

 that are mostly wind or self-fertilised. 



2. Corydon, Avion, Minima, Bellargus, Hyale, Edusa, Aurinia, 

 Cardiil, feeders on low plants mostly cross-fertilised. 



