4 
AMERICAN SPECIES OF ARADUS (hEMIPTERa) 
a novel and uncrowdcd haliitat under the liark on which he had 
previously lived, protected in some degree from hostile observa- 
tion by concealing coloration, and in this seemingly ill-favored 
environment, become most suitalile In the lapse of time, the 
race has prospered, develoiiing numerous species and achieving 
a world-wide distrilmtion. More intimate adaptation could 
hardly be imagined than that which these insects now exhibit, 
and it seems indeed difficult to reconcile with such conditions a 
theory of evolution which dogmatically bids us eliminate from 
consideration any formative or modifying influence of the im- 
mediate surroundings; on the contrary the imiircss of the en- 
vironment is manifest in every feature of the group. There 
are some, however, who find it easier to believe in chance adapta- 
tion of the animal liefore it has found its fitting place in the 
scheme of things, and very likely botfi processes have had a 
share in producing every case of observed adaptation, since there 
is nothing essentially antagonistic in the two views. The old 
memories still live in the race, notwithstanding the changes which 
have been affected in the course of time, for in the first warmth 
of siiring obscurity loses its charm for a brief season and the 
insects emerge and appear on the surface of the bark, where the 
ancestral coloration still serves to make them invisible, and they 
fly actively in the sunshine, seeking new and distant homes in 
obedience to the universal instinct of migration. 
Pterygo-polymorpiiism 
This iiower of flight is not shared, however, by all individuals, 
for, as in many other Hemipterous families, certain species ai'e 
pterygo-i)olyniori)hic, presenting more or less commonly brachyi)- 
terous individuals which lack functional hind wings and exhibit 
ri'diiction in the hemielytra, with concomitant modification of 
the prothorax, within wdiich certain muscles of flight are atro- 
phied. In Ai'ddm this reduction is variously ix'lated to sex and 
is manifested in tw'o ways: by abbreviation of the hemielytra, 
or true brachyptery, and by extriMue attenuation without loss 
in length, which may Ix' tm-med stmiojiti'ry. In both cases the 
hind wings aix' vestigial or absent. Occasionally we meet with 
individual cases of partial bracdiyjitmy, with hind wings present. 
