“SEPTEMBER 10, 1897.] 
even with the others which Mr. Wallace 
has termed ‘obscure and uninteresting,’ 
when, owing to the indefatigable industry 
of entomologists as a class, important facts 
can be gained along distribution lines from 
the group of insects. Thus it is only within 
the past few months that the publication 
of Mr. W. F. Kirby’s ‘Catalogue of the 
‘Odonata of the World’ has made it possible 
for Mr. G. H. Carpenter, of the Royal Dub- 
lin Society, to prepare a comprehensive 
paper on the geographical distribution of 
the dragon-flies, a group in which a com- 
paratively few workers have interested 
themselves. It is in a measure true to-day, 
as it was entirely true when Wallace wrote, 
that ‘‘many of the groups are so liable to 
be transported by accidental causes that 
they afford no useful information for our 
subject,”’ yet even with the group in which 
the greatest obscurity as to the original 
home of the species has existed, owing to 
a very easy and most frequent commercial 
transportation—the Coccidz or scale-in- 
sects—the continued discovery and char- 
acterization of new forms from all parts of 
the world, and especially of those existing 
in wild regions, away from the influence of 
man, are gradually giving us an insight 
into the probable character of the original 
coccid faunas of more or less restricted re- 
gions. 
By reason of the drawbacks mentioned, 
Wallace considered only ‘‘a few of the larg- 
est and most conspicuous families which 
have been so assiduously collected in every 
part of the globe and so carefully studied 
at home as to afford valuable materials for 
comparison with the vertebrate groups.’ 
These groups included 16 families of diur- 
nal Lepidoptera and six of the families of 
Coleoptera. Even with this restriction 
among the beetles, however, he must have 
had some difficulties with the accidental 
importations, for among the beetles are 
hundreds of examples of this class of intro- 
SCIENCE. 
387 
ductions. For example, writing later in 
his Island Life, the great naturalist shows 
that in 1880 the total number of species of 
beetles known in the Azores amounted to 
212, of which 175 were European. Outof 
these, however, no less than 101 were be- 
lieved to have been introduced by human 
agency. Concerning St. Helena he quotes 
Mr. Wollaston’s opinion that 74 of the 203 
species have certainly been introduced by 
the agency of man. 
In considering the question as to the re- 
gions with which an interchange of forms 
is most likely to occur, it is obvious that 
they are those which have the greatest sim- 
ilarity of climate, and, most nearly, iden- 
tity in point of time of seasons, those in 
fact which are most likely to afford similar 
environmental conditions. A study of the 
similarity of faunas and floras already ex- 
isting will lead us to the same result. 
Wallace has pointed out that with the Cole- 
optera the best marked affinities between 
regions are those between the Nearctic and 
the Palearctic, the Oriental and Australian, 
the Australian and the Neotropical, all of 
which appear to be about equal in each ease. 
Next comes that between the Ethiopian and 
the Australian on the one hand and the 
Ethiopian and the Neotropical on the other, 
which also appear about equal. Then fol- 
lows that between the Nearctic and Neo- 
tropical regions, and lastly, and by far the 
least marked, that between the north tem- 
perate and south temperate regions. 
Further, in the consideration of acci- 
dental commercial importations, theamount 
and frequency of commercial interchange 
and the rapidity of the journey are most 
important factors. 
From all of these considerations com- 
bined we arrive at the conclusion that the 
regions with which accidental interchange 
of species should be most frequent are 
Europe and North America, and this is 
with insects to a certain extent borne out 
