192 ENTOMOLOGICAL SOCIETY 
erns the introduction or non-introduction of each species a factor 
which is variable according to each species and over which man 
has no control and is likely never to have any. Look at the re- 
corded introduction of European species which, as stated before, 
are so readily transported into North America. There are many 
examples where the introduction of very common species has not 
taken place at all, or where it suddenly takes place after 400 years 
of non-introduction, or where introduction has taken place under 
the most improbable circumstances. There is a common Euro- 
pean fly, Eristalis tenax, which in the larva state lives in all 
sorts of dirty and slimy places, so as to present the most readily 
available species for transportation and introduction into North 
America. Still it has taken nearly 400 years to accomplish this 
introduction, and when it was finally accomplished the species 
spread with incredible rapidity all over the United States. I men- 
tion this sample of the Order Diptera, because Baron Osten Sac- 
ken has given us a most interesting paper on the intricacy of this 
subject, published in the Transactions of the London Entomologi- 
cal Society for 1884. There is in Europe a common ladybird, 
Coccinella j-punctata^ in habit very much alike to C. bipunc- 
tata, which has long since been introduced here. Still the former 
has never shown any disposition to become Americanized, al- 
though it has probably more than once been brought in ships to 
our shores. This instance is paralleled in the European Sar- 
cophaga carnaria. Numerous examples may be brought forth 
to show that successful introduction has taken place under rather 
improbable conditions e. g, , \nPhlceotrya Vaudoueri. This 
is a rare species, apparently not belonging to the circumpolar 
fauna, and which occurs in southern France, its larva probably 
living in the decaying wood of forest trees. Still, it must have 
been imported at some time, and is now to be found in many 
widely separated localities in the United States. Many European 
species of the genus Philonthus and other large genera have found 
their way to North America. Many other equally common spe- 
cies have hitherto refused to be transported and introduced. Many 
of the introduced species have spread with great rapidity e. g., 
Scolytus rugulosus, which, being evidently a recent importation, 
occurs now from Georgia to Ohio and northern New York. 
Hylesinus trifolii, also recently introduced, extends now from 
