STATES OF INSECTS. (Larva.) 147 
described. It is cylindrical, slightly thinner at the apex, 
which is obtuse, fleshy, incapable of motion, of a black 
colour, and about two lines long. On the same segment, 
also, in the case-worms (Trichoptera) are three fleshy 
conical eminences, which the animal can inflate or de- 
press, so that they sometimes totally disappear, and then 
in an instant swell out again. When retracted, they form 
a tunnel-shaped cavity, varying in depth*. Reaumur 
conjectured that these eminences were connected with 
respiration, and one circumstance seems in favour of this 
conjecture, that this segment has not the respiratory 
threads observable in the subsequent ones. Latreille 
mentions certain fleshy naked eminences placed upon 
the ninth and tenth segments of some hairy caterpillars, 
which, like those just mentioned, the animal can elevate 
more or less. ‘They are often little cones; but when it 
would shorten them, the summit is drawn in, and a 
tunnel appears where before there was a pyramid>. 
In a former Letter I gave you a short account of the 
remarkable Y-shaped, as it should seem scent-organs, 
(Osmateria) of the beautiful caterpillar of the swallow- 
tailed butterfly (Papilio Machaon), and others of the 
Equites* ; I will now speak of them more fully. That 
found in the former is situated at the anterior margin at 
the back of the first segment, close to the head, from 
which at first view it seems to proceed. At the bottom 
it is simple, but divides towards the middle, like the let- 
ter Y, into two forks, of a fleshy substance‘, which it 
can lengthen, as a snail does its horns, to five times their 
@ De Geer ii. 507. ¢. xi. f. 16. mn. t. xiv. f. 7. 
> N. Dict. d’ Hist. Nat. vi. 256. 
“ See above, Vot. IL. p. 244—. 
¢ Plate XIX. Fie. 1. a. 
LZ 
