[ 286 ] 
26 
or more ; and we often find them in isolated situations and under 
circumstances which preclude the idea that they could ha\e been 
brought hither by human agency. For example, the Oyster-shell 
Bark-louse, being an imported insect, is never found, in a state of 
nature, upon our native crabs, and when they accidentally get a 
foothold upon them they do not multiply much, the crab tree be¬ 
ing evidently uncongenial to their tastes. Yet I have seen them 
in small numbers upon every tree of a small grove of crab-apples 
which I have known for twenty-five years, standing upon the 
prairie, nearly a quarter of a mile from any apple orchard; and I 
have found a few scales on another crab-apple tree standing in 
the edge of the timber, more than half a mile from any cultivated 
trees. " The bird theory, however, is a very inadequate one to ex¬ 
plain the general diffusion of the Bark-louse. The most we could 
expect would be that a few of the insects might possibly be thus 
transported during the short time when they are not attached to 
the tree; and a series of experiments which I made, the past sea¬ 
son, with the view of testing this theory, go to disprove the. sup¬ 
position that they are ever disseminated in this way. I wished 
to see whether these minute insects would readily crawl on to any 
obstruction like the toes of a bird. I experimented for hours by 
putting little slivers of wood about as large as a bird s claw in the 
way of the crawling Coccids, but in no instance would they crawl 
on to them. If the stick were put down abruptly before them, at 
a short distance, say one-tenth of an inch, they would usually stop 
and turn off in another direction, showing that they have the 
sense of sight. If it were put a little further off, so that they 
would approach it gradually, they would sometimes turn away 
before reaching it, and at other times they would come up to it, 
run along parallel to it, and if they could not find a place to get 
under it, they would turn away. I then beveled off the stick tc 
a sharp edge, so as to present the least obstruction, and at the 
same time offer an inclined plane up which they could easily crawl, 
but they would not go on to it. It is pretty evident, therefore, thal 
these creatures have no instinct which leads them to avail them 
selves of such means of transportation. 
The third theory is that they are blown from place to place b) 
the wind. That they are carried by a moderate breeze, during 
their hatching period, to a distance of several rods, has beer 
abundantly proved by myself and by others. It you suspend ar 
