PSF CLE: 209 
Psocus venosus Burm. 
The species is found everywhere from 
Canada down to the Gulf of Mexico and 
occurs also in Cuba. I do not know 
whether it is found west of the Rocky 
Mountains or not. It appears to live 
gregariously, sometimes in large num- 
bers, on apple trees, in all different 
stages. As it is here the largest species, 
I have tried to study it carefully, and 
give here a short notice of some entirely 
new characters, which may be observed 
partly in other species. 
The wings of Psocus have mostly 
been treated of in a rather summary 
manner. The venation is considered in 
a different way by different writers, but 
a satisfactory study of the species not 
belonging to the European fauna has 
thus far been wanting, and such a study 
will probably lead to better knowledge. 
I use here, for convenience, the nomen- 
clature adopted by Mr. Kolbe in his new 
monograph, reserving until a future time 
and as the result of farther advanced 
‘study, the introduction of some changes. 
I would here draw attention to a few char- 
acters, which I find nowhere mentioned. 
1. At the extreme base of fore and 
hind wing of Psocus venosus (and several 
related species), just below the the sub- 
costa, there is a darker, more chitinous 
place, bordered below by the median 
vein and ending in front about where 
the submedian begins. Examined witha 
rather strong lens, this place (0.2 mm. 
long) has the appearance of a sieve 
with numerous round holes of 0.003 mm. 
diameter, arranged in a series of longitudi- 
nal lines, not strictly keeping in the lines. 
In changing the focus, every hole is found 
to have a small sensitive bristle in the 
centre. The whole arrangement is simi- 
lar to that on the base of the wings of 
diptera or on the antennae of insects, 
described long ago, and presumed to 
represent the sense of hearing. I have 
hitherto been unable to prove the pres- 
ence of nerves and ganglia in this place, 
but such will be found without doubt. 
In full grown nymphae I was able to see 
the same arrangement, but in a less 
definite shape. The small holes have not 
such sharp borders in the nymphae as in 
the imagos, and the middle elevation 
seems to be larger than in the imago. 
2. The wings of full-grown nymphae, 
while still contained in the wing case, 
show nearly the whole venation indicated 
by paler lines, representing the veins, 
which are blood vessels. Around the 
margin of the whole forewing runs a 
broad sinus (0.016—-0.023 mm.), with 
which the other veins are connected. 
The whole wing is dull, not hyaline, pale 
grayish, densely filled with cells. The 
tracheae are very small (0.0017 mm. 
diameter against 0.005 in the imago), 
often only indicated, and the spiral thread 
not visible or replaced by transverse 
nuclei. In an earlier stage there is found 
as the first indication of a trachea, one 
series of cells arranged ina band. The 
trachea forming the analis of Kolbe is 
always broader (0.0025 mm. diameter, 
against 0.083-+ in the imago). The 
analis belongs to the underside of the 
wing and is, as far as I know, the only 
one not accompanied by a blood vessel, 
and formed only by a trachea for pur- 
poses later to be spoken of. The hind 
border of the wing case has two series 
