STATES OF INSECTS. (Larva.) - 149 
bability is, that they essentially differ. ‘Two globose re- 
tractile vesicles issue from the ninth and tenth segments 
of those of Arctia chrysorrhaa, &c.* 
A great number of Lepidopterous larvee, particularly 
those which are smooth and of a moderate size, have 
between the under-lip and fore-legs a slender transverse 
opening, containing a teat-like protuberance of the same 
construction as the furcate horn of the caterpillar of the 
beautiful mountain-butterfly, Parnassius Apollo ; and, 
like that, can either be wholly retracted and concealed, 
or by pressure be extended to the length of one of the 
legs. In some larvee this part is of a subhemispherical 
figure, generally single, but sometimes double. It is 
commonly, however, more slender and conical; and 
when of this shape, it is sometimes quadruple. The 
use of this part is not very clearly known: some have 
supposed it to be a second spinneret, and to be of use in 
fabricating the cocoon; but it is more probable that it 
secretes some other kind of fluid, and is connected with 
defence. 
The singular organ in a similar situation, evidently 
for that purpose, with which the puss-moth endeavours 
to annoy its assailants, has been described in a former 
Letter, to which I refer you’. Bonnet, who was the first 
that discovered this organ, ascertained that it might be 
cut off without injury to either larva or imago. He also 
remarked in a caterpillar found in the wild succory 
(Cichorium Intybus) another short, black, needle-shaped 
organ between the conical part just described and the 
under-lip*. De Geer mentions a remarkable fleshy 
* Reaum. 1. 92. >» Bonnet ii. 84—. iit. 1, 
“ See above, Vou. II. 251—. 4 Bonnet ii. 88, 
