592 The American Naturalist. [July, 
any unusual feature of the mouth structure. In giving the characters 
of the order, he says: “The mouth-parts are probably used chiefly for 
sucking ; they are intermediate in form between those of the sucking 
and those of the biting insects; the mandibles are bristle-like ; the 
maxillæ are triangular, flat, and furnished with palpi; the labial palpi 
are also present.” 
I have just examined a copy of Jindrich Uzel’s “ Monographie radu 
Thysanoptera,” 1895, perhaps the most extensive work yet published 
on the Thysanoptera, in which the view of the mouth structure de- 
scribed by me in the Bulletin of the Essex Institute and before the 
Entomological Club is adopted, though Uzel is disposed to take a dif- 
ferent view of the homology of the unpaired mouth-part. His words 
are (Ibid, p, 25): “In der Höhlung des 
Mundkegels bewegen sich die Mondibeln 
in Form zweier Stechborsten und der 
unpaare Mundstachel (wohl ein umge- 
bildeter epipharynx) welcher linker- 
seits liegt und den fiir die Thysanop- 
teren characterischen Unsymmetrischen 
Bau der Mundwerkzenge bedingt.” In 
order to show more clearly what the un- 
paired part is like, I have made a draw- 
ing from his Figure, 161, Tab.: IX, 
which is here reproduced. 
Of the interpretation Uzel is disposed 
to put upon the unpaired part, I have 
only this to say: It is plainly closely 
adapted to the left side of the head, and 
the parts belonging to the region in 
which it lies are closely adapted to it. 
It is very evident that it was made. to 
fit in the angle formed by the hard parts 
: bali ' of the head on the left side; the labrum 
is, on this side, shortened and: otherwise suited to accommodate it... A 
reéxamination of my slides shows the adjustment more complete even 
than represented in Uzel’s figure. Coupled with this is a manifest. de- 
ficiency in the head on the right side at the place where.a correspond: 
ing structure should be. ; It is evident that something is lacking on the 
right side. Ifthe unpaired organ is an epipharynx that has been diss 
placed, why should the cranial structure of the right side be altered? 
Pe peoa 
