402 THE INSECTA. §$ 328. 
traordinarily complicated, that it is very difficult to recognize its elements. 
When horny, there can always be distinguished an epidermis composed of 
unnucleated, lamellated cells intimately blended together. These cells, 
however, are often polyhedral, and go disposed as to form a simple layer ; 
in other cases, they are more or less blended together, giving rise to undu- 
lating or imbricated lines in the epidermis. In crder to study the subjacent 
layer, or dermis, the cutaneous envelope must be macerated and decolored 
in caustic potass. This layer will then be found to be composed usually 
of several lamellae superposed in various ways and thereby often producing 
very elegant markings. In many instances, these reticulated or radiated 
markings would indicate the presence here of intercellular passages, and 
porous canals.” In the thin, membranous portions of the skeleton, for 
instance, the wings, the structure usually appears wholly homogeneous. 
On the external surface of this envelope there are 0 en numerous ex- 
crescences, such as tubercles, spines and hairs, which are usually hollow. 
The hairs are sometimes simple and smooth, sometimes set with small hairs 
or barbellate.” Many of these cutaneous formations are inserted by a 
small peduncle in small fossae, to which they loosely adhere, and from 
which they are very readily detached. Usually, they are flattened, scale- 
1 Histological researches upon the cutaneous 
skeleton have, as ‘yet, been extended over only a 
few species. I am able to cite only the works of 
Hi. Meyer (Miller’s Arch. 1842, p. 12 (Lucanus 
cervus), and of Platner (Ibid. p. 38, Taf, III. 
{Bombyx mori). . 
2 These barbellate hairs are found with the lar- 
vae of all the Bombycidae (Réaumur, Mém. Xe. 
Tom. I. Pl. VI., and Degeer, Abhandl. I. Taf. 
1IX.-XIII.). x 
They are easily rubbed off, and when brought in 
contact with our skin, they insinuate themselves 
by the truncated extremity, and thereby often pro- 
voke an insupportable itching or even an inflamma- 
tion. The processionary moths are so much feared 
in this respect as to pass for being poisonous ; see 
Nicolai, Die Wander-oder Prozessionsraupe, 1833, 
p. 21,and Ratzeburg, Du Forstinsekten, II. p. 
127, Taf. I. fig. 11, 12, and Taf. VIII.« The 
‘pains which these hairs can produce with man, may 
be judged by the disease which Ratzeburg suffered, 
and of which he has given an account (intom, 
Zeit. 1846, p. 35). 
The symptoms spoken of by this excellent ento- 
mologist may be explained without attributing any 
specific poisonous property to these hairs, if it be 
considered that, like a fine powder, they rest on the 
skin and may enter the respiratory organs by 
inhalation, and penetrating the tissues encoun- 
ter a multitude of nervous fibres. heir passage 
into the tissues is the more easy, since they are 
_ fusiform, very sharp at both extremities, the free 
* [§ 328, note 2.] Will (Schleiden and Fro- 
riep’s Not. 1848, Aug. p. 145) has made chemico- 
micr pical inv upon the nature of this 
peculiar poisoning power manifested in the proces- 
sionary moths ; his researches were upon Bombyx 
processionea. The poisonous material was found 
to be formic acid in a free and highly-concentrated 
tate ; it was met with in all parts of the cater- 
pillar, but especially in the faeces, in the greenish- 
yellow liquid emitted by these animals when di- 
one of which is provided with denticulations point- 
ing upwards, while the opposite one is loosely in- 
serted in a small fossa, so that they are detached 
without breaking from their fastenings by the least 
contact. The deep-colored spots observed on the 
back of the processionary moths, and which are di- 
vided into four parts by crucial lines (Ratzeburg, 
Die Forstinsekt. loc. cit. Taf. VIII... fig. 1.4 and 
1.!), consist of callosities on which are situated 
thousands of these small fossae from which arise an 
infinite number of hairs. With many birds and 
insectivorous reptiles, the hairs of the moths which 
these animals have eaten, traverse the mucous 
membrane of the stomach and enter the tissues. 
I should not have thus mentioned this subject, 
since for a long time the true nature of the hairy 
stomachs of old cuckoos has been understood (see 
the discussion on this subject between Brehm, 
Richter, Carus, Oken, and Bruch, in the Isis, 
1828, p. 222, and 666, Taf. VIII., also, 1825, p. 
579, Taf. IV.), if, recently the passage of hairs 
from the digestive tube into the mesentery of frogs 
had not given rise toa similar error. The mesentery 
of these reptiles very often contains fragments of 
hairs and the spines of insects, surrounded by con- 
centric layers of connected tissue and thus arrested 
in their course. These encysted hairs have been 
described by Remak (Muller’s Arch. 1841, p. 
451) under the name of parasitic enigmatical horny 
fibres, while Mayer at Bonn has gone so far as to 
take them for Pacinian corp Die Pacinisch 
Korperchen, 1844, p. 14, fig. 2).* 
vided, and in the hairs. These hairs were mostly 
hollow, and their cavity was not closed at their 
base, but passed through the skin and appeared 
connected with glands below. These observations 
are the more interesting since this same observer has 
shown that the poisonous material of the poison- 
apparatus of the Hymenoptera, consists likewise 
of formic acid. See my note under § 347, note 
11. — Eb. 
