126 Annals Entomological Society of America [Vol. VIII, 
An insect that belongs to a country through inheritance, and 
one that it obtains through migration or dispersal, each may 
spread over that country and exist side by side; or each may be 
restricted to a very narrow range. The many cases of insect 
introduction in historic times show that great numbers of insects 
not now occurring here, could live and thrive with us. 
The various orders, families, and genera of insects did not 
originate at the same time and place. The place of origin, and 
the changes that have elapsed since their origin have a definite 
bearing on their distribution today. Most divergent views of 
the relationship of certain faunas are often expressed by stu- 
dents who consider different groups. For example the Panorpid 
fauna of the United States would show that the Eastern United 
States is closely related to Europe, while the Raphidiide would 
show that it is the Western United States that is related to 
Europe. Again the large and rather recent family of butter- 
flies, Heliconide, are only neotropic; while the ancient, small, 
family Sialide are of world-wide occurrence. The explanation 
must be in the different time and place of origin of these groups, 
and the continental changes that have aided or barred their 
dispersal. 
From a study of mammals and birds zoologists divide up the 
world into several zoological realms, whose outlines agree fairly 
well with those of the continents; thus we have an African, 
Australian, South American, Malayan, Indian, and Holarctic 
realms; the latter for Europe and North America. With 
insects this is not so. Several, probably all, of the continents 
possess elements showing relationship to other regions, deriv- 
atives of a fauna more fully developed elsewhere, and indicating 
that insect distribution is much older than the present form of 
the continents. Thus the Nearctic part of the Holarctic realm 
is not a unit, but a commingling of natives and immigrants from 
times long before there were any mammals. 
New Zealand has been included in the Australian realm, yet 
the insect fauna of New Zealand is more foreign to Australia 
than to America. Moreover, Australia presents at least two 
very different series of insects, one similar to that of Europe or 
at least to the fossil insects of Europe, and the other a series of 
peculiar, often primitive forms entirely unlike the European 
insects. 
