‘| Seg sg) WS Syl ox eh ae 
SOME PSOCINA OF THE UNITED STATES. 
BY HERMANN AUGUST HAGEN, CAMBRIDGE, MASS. 
(Concluded from p. 210.) 
3. Pterostigma-hook. ‘Vhis curious 
feature has until now been entirely over- 
looked. It is mostly ‘‘ the small black 
or dark spot at the basis of the ptero- 
stigma” mentioned in the description of 
the species. Apparently low magnify- 
ing powers have always been used in the 
study of Psocus. The subcosta of the 
fore wings always goes to the mediana, 
except in Amphientomum and related 
genera, Perientomum, Syllisis, Calopso- 
cus and other exotic forms, where the 
subcosta joins the costa. Sometimes the 
subcosta ends abruptly, without joining 
one of the two adjacent veins. Whether 
this vein is analogous to the subcosta, 
as McLachlan contends, or whether it is 
only a branch of the subcosta similar to 
that in Calotermes and other insects, is 
still a point of dispute. + I never saw it 
accompanied by a trachea, nor, as far 
as my observation goes, have I seen 
a trachea accompanying the costa from 
the base of the wing to the pterostigma. 
The mediana is accompanied by a very 
strong trachea from the base to the ptero- 
stigma. This trachea is not contained 
in the vein, but runs very near it, below, 
sometimes indeed separated from it a 
little, so that two veins seem to be 
present here. At the beginning of the 
pterostigma the trachea has a spindle-. 
shaped, more or less long dilatation, a 
tracheal bladder, with visible but more 
separated spiral threads. This dilata- 
tion lies below a small sac or better a 
hernia of the mediana, before it enters 
the large sac or blood sinus represented 
by the pterostigma. This hernia is not 
developed in the wing of the nympha, 
but just after transformation it is found, 
as well as the pterostigma, crowded with 
blood cells. The hernia is found, some- 
times very visible, in most of the genera, 
except in a few aberrant groups such as 
Amphientomum and its relations, Em- 
pheria and perhaps others. There the 
spindle-shaped tracheal bladder is pres- 
ent, but simply follows the end of the 
mediana to the costa. Where the her- 
nia is present, it lies on the under side 
of the wing, where the mediana enters 
the costa, and forms together with it the 
pterostigma. Probably the stronger cur- 
rent in the costa somewhat opposing the 
current of the mediana is the reason of 
the formation of the hernia, to overcome 
the pressure of the current in the mediana. 
As everywhere in insects where strong 
currents occur, accompanied by strong 
tracheae, we find here the tendency to a 
more prominent chitinization. There- 
fore the hernia shows very different 
forms, a ball, a circular or bottle-shaped 
inflation or a more or less chitinous and 
dark-colored often sharp hook, as in 
Oaecilius, Peripsocus and others. In 
Psocus (proper) it has mostly the shape 
