306 ENTOMOLOGY 



Geographical Varieties. Darwin found that wide-ranging species 

 are as a rule highly variable. The cosmopolitan butterfly Vanessa 

 cardui presents striking variations in different parts of the earth, largely 

 on account of climatal differences, as is indicated by the temperature 

 experiments of several investigators. Standfuss exposed German pupae 

 of this insect to cold, and obtained thereby a dark variety such as occurs 

 in Lapland; and by the influence of warmth, obtained a very pale form 

 such as occurs normally in the tropics only. Our Cyaniris pseudargiolus, 

 which ranges from Alaska into Mexico and from the Pacific to the At- 

 lantic, exhibits many geographical varieties, some of which are clearly 

 due to temperature, as experiments have shown. 



Geographical isolation is often followed by changes in the specific 

 characters of an organism, as witness the endemic species and varieties 

 of oceanic islands. Even in the same archipelago, the different islands 

 may be characterized by different varieties of one and the same species, 

 or even by different but closely allied species of the same genus. Thus 

 Darwin and Alexander Agassiz found that in the Galapagos Islands each 

 island had its own species of Tropidurus (a lizard) and had only one 

 species, with almost no exceptions. The same phenomenon occurs in 

 the two Galapagan species of Schistocerca 5. melanocera and S. literosa. 

 In melanocera, as Scudder discovered, "Three or four distinct types are 

 becoming gradually differentiated on the eight [now ten] islands from 

 which they are known." Snodgrass, who has made important addi- 

 tions to Scudder's account, says, in regard to the two species, "The 

 specimens from the different islands show striking, though, in most cases, 

 slight differences distinguishing the individuals of each island as a race, 

 from those inhabiting any other island. There are two exceptions. 

 Abingdon and Bindloe have the same form, and Albemarle supports at 

 least two races. " Each of these two species presents no less than five 

 racial types, to which distinctive names have been applied. Though 

 the relationships and evolution of these races have been ably discussed 

 by Snodgrass, definite conclusions upon these subjects are still needed. 



Faunal Realms. The general distribution of life is such that 

 naturalists divide the earth into several realms, each of which has its 

 characteristic fauna and flora. As to the precise boundaries of these 

 faunal realms, zoologists do not all agree, owing chiefly to the fact that 

 faunae overlap one another to such an extent as to render their exact 

 separation more or less arbitrary. Five realms, at least, are generally 

 recognized: Holarctic, Neotropical, Ethiopian, Oriental and Australian 

 (Plate III). 



