fe, OS 
PSYCHE. 221 
It is easily understood why only the anal 
vein of the under membrane is strongly 
developed. This alone has to work in 
keeping the hind wing in place. As the 
two membranes of the wing are very 
loosely connected one to the other, it is 
an apparent advantage that just the 
working vein is more strengthened at 
the expense of its not-working partner. 
The lock becomes even stronger by the 
connection of the axillary vein at the same 
place on the hind margin. In Ps. veno- 
sus the diameter of the anal vein is about 
0.176 mm., and the side projection of 
the spiral thread about 0.059 mm. 
Where the anal vein connects with the 
axillary vein, which is more chitinized 
at its end, there is a strong yellow chi- 
tinous hook, its opening about 0.333 mm. 
looking to the tip of the wing. At first 
the hook looks as if it was only the pro- 
longation of the spiral threads, as it con- 
sists of numerous fine threads in near 
juxtaposition; its tip is bent, flat and 
transversely cut. But a closer examina- 
tion shows that the hook originates, with 
numerous roots, from the upper margin 
of the axillary vein, and one stronger, 
straight root from the inferior margin. 
A transverse row of four small, horny 
teeth in crescent shape is placed just 
opposite the opening of the hook on the 
end of the axillary vein. It is well 
understood that the anterior margin of 
the hind wing, caught in the hook, 
and assisted by these teeth, will be held 
firmly in position. But to facilitate the 
catch the margin of the fore wing just 
opposite to the hook is bent downward, 
and allows the margin of the hind wing 
to slide in an easy manner in the hook. 
To make things stronger and more 
efficient, the point by which the hind 
wing is caught in the hook is just where 
the interior ramus (Kolbe) of the median 
vein originates, and I have reason to 
believe that not only the front margin of 
the hind wing, but also the median vein, 
is placed in the hook. At least several 
specimens of Psocus in amber show such 
a position. 
The lock is about the same in Psocus 
nebulosus and related species. Ps. affinis, 
in amber, has numerous transverse im- 
pressions above the end of the axillary 
vein, forming a row of teeth to take hold 
of the hind wing. Caecilius and Epi- 
psocus possess a hook similar to Psocus, 
but more pointed; Amphientomum has 
the end of the axillary vein bent up, and 
a tubercle on the anal vein. Probably 
there will be a difference in the lock of 
other psocina. 
5. Mouth-parts. 
The mouth-parts of Psocus were de- 
scribed in a satisfactory manner generally 
by Latreille nearly a century ago. The 
valuable details given recently, chiefly 
concerning the maxilla, have not men- 
tioned the most interesting fact, that the 
inner lobe (fork, Burgess) slides in the 
outer lobe as in a vagina. The fact is 
easily ascertained in living specimens, 
and, if the preparations are not com- 
pressed so much as to separate the parts, 
in alcoholic specimens. Latreille says: 
‘‘altera (parte mandibulae) externa 
membranacea, vaginam constituens cy- 
lindrico compressam, obtusam, apice per- 
vio.” It should be acknowledged that 
the figures published by Latreille are 
very faulty, and correspond in no way 
with the description. Fabricius has 
described the parts ‘‘ maxilla cornea, 
