ZO 
of long bristles (0.104 mm. long). 
Specimens just after transformation 
show the wings hyaline but somewhat 
milky. The larger veins and the ptero- 
stigma are filled with a large number of 
blood-cells. The two membranes of the 
wings, even in the imago state, are less 
firmly glued together than in other 
insects, and easily separated if the wing 
is touched roughly or glued with one 
side on paper or glass. The membranes 
of the hind wings are still less firmly con- 
nected than those of the forewings. In 
going through a moderately large collec- 
tion of Psocus, specimens will be found 
showing a separation of the two mem- 
branes at least in some parts. The same 
is often to be seen in fossil species 
included in amber or in copal. 
All veins show numerous short ap- 
pressed hairs, the longest on the margi- 
nal vein around the wing (0.009 mm. 
long). The only vein without any cloth- 
ing of hairs is the analis. The whole 
membrane of the wing is beset more or 
less densely with similar but much smaller 
hairs (the longest 0.003 mm.). 
It is a fact new to me that the 
whole venation, with the exception of 
the subcostalis and analis, consists of a 
double net, not only of veins, as I have 
proved long ago, but also of tracheae, 
one net belonging to the upper mem- 
brane, the other to the lower one. Both 
are exactly alike and cannot be seen 
when the two membranes are firmly glued 
together. When separated, which oc- 
curs more easily in the hind wings, both 
nets are clearly visible, and each trachea 
of the upper membrane joins the corres- 
CSITCHE . 
ponding one of the lower membrane in 
a loop at the margin. I have to remark 
that the tracheae seem only in juxtapo- 
sition to the blood veins, at least I have 
established this undoubtedly in the case 
of the mediana. A more detailed study 
of the origin of the veins will probably 
give a more certain basis of facts for 
identifying the value of the veins, and 
a better founded 
For instance, the ramus 
medianae interior in the hind wings is 
united with the ramus submedianae exte- 
rior at the base of the wing, and both 
can only be considered to be the two 
In the fore- 
wing the ramus medianae interior is a 
branch of the mediana and the ramus sub- 
medianae exterior a branch of the subme- 
The mediana originates from the 
anterior basal wing-callus, the submedi- 
ana from the posterior wing-callus ; nev- 
ertheJess both veins are connected by a 
tracheal loop at the extreme basis of the 
wings. I have purposely given this in 
such detail, because the whole disagree- 
ment about the nomenclature of the veins 
between McLachlan and Kolbe consists 
in this point. But I have not yet fin- 
ished my studies to a point satisfactory 
to myself, so as to emit a positive opinion 
about those veins. 
The somewhat loose connection of the 
two membranes of the wings, and the 
fact that the tracheae are double and 
constitute, for a very large part, the 
venation, easily explains the very fre- 
quent variations and warns us to use such 
differences only or chiefly for generic 
separation. ( To be continued.) 
for contributing to 
nomenclature. 
branches of the same vein. 
diana. 
