90 
ORIGIN OF LIFE IN AMERICA 
less than a hundred and twenty-two species found in temperate 
and northern Europe, and also in North America, reasoning 
that since the greater number of them also live in northern 
Asia they must have spread from one continent to another 
across Bering Strait. He does not definitely state that he 
considers the Strait to have been a land surface at the time 
these species are supposed to have passed across it. Still he 
emphasises the intimate relationship of the Alaskan and the 
opposite Siberian shore fauna, by citing the names of four 
species of Ilemiptera which are confined to these two 
countries. 
A rather striking example clearly illustrating the gradual 
advance of a genus across Asia, and its final immigration 
into North America, is shown by Parnassius, a genus of 
butterflies to which the European “ Apollo ” belongs. The 
Apollo group of butterflies originated, according to Mr. 
Austaut, towards the latter part of the Tertiary Era in Asia, 
at the time when some of the great mountain chains of that 
continent were being formed. I alluded to the European 
species of Apollo in my work on European Animals, gave a 
map of their distribution and enlarged upon their origin. I am 
in full agreement with Mr. Austaut’s views as to the Asiatic 
centre of dispersal. The only point in which I differ is with 
regard to the period of its origin, which I believe to have 
been considerably earlier than Mr. Austaut* thinks likely. 
In Europe we possess only three species of Parnassius, 
whereas there are thirty-five in Asia, Turkestan being the 
richest country in Apollos. Some species are peculiar to the 
Altai Mountains in Siberia, and as we go eastward new forms 
replace those with which we had become familiar. In Amur- 
land there are others, and yet when we cross Bering Strait to 
Alaska we still meet with an Apollo (P. nomion) which also 
occurs in the Altai Mountains, while the Californian Apollo 
(P. clodius) is very closely related to Parnassius clarius of 
these same mountains. The Asiatic character has thus been 
retained by two of the American species. Two others, Par¬ 
nassius thor of Alaska and Parnassius sminthus, are quite 
distinct from any others, indicating that the passage from 
* Austaut, J. L., “ Les Parnassiens,” pp. 62—63. 
