402 



THE INSECTA. 



^323. 



traordinarily complicated, that it is very difficult to recognize its elements. 

 When horny, there can always be dlHtinguished an epidermis composed of 

 unnucleated, lamellatcd colls intimately blended together. These cells, 

 however, are often polyhedral, and so 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 order to study the subjacent 

 layer, or dermis, the cutaneous envelope nmst 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, ibr 

 instance, the wings, the structure usually appears wholly homogeneous. 



On the external surface of this envelope there are o 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 

 H. Meyer (^Muller''x Arch. 1842, p. 12 (Lucanus 

 cervus), and of Plainer (Ibid. p. 38, Taf. III. 

 {Bombyx mori). 



'i These barbellate hairs are found with the lar- 

 vae of all the Bombycidae (Reaumur, M(5m. &c. 

 Tom. I. PI. VI., and Degeer, Abhandl. I. Taf. 

 LX.-XIII.). 



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 

 Nicolaj, Die Wander-oder Prozessionsraupe, 1833, 

 p. 21, and Ralzeburg, 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 Ralzeburg suffered, 

 and of which he has given an account (Entom. 

 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. Their passage 

 into the tissues is the more easy, since they are 

 fusiform, very sharp at both extremities, the free 



one of which is provided with denticulations point- 

 uig 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 {Ralzeburg, 

 Die Forstinsekt. loc. cit. Taf. VIII. u tig. l.i- and 

 1. '), consist of callosities on which are situated 

 thousands of these small fossae from which arise an 

 infinite number of hairs. Witli many birds and 

 insectivorous reptiles, the hairs of the moths which 

 these animals liave 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, 

 Richler, Cams, Oken, and Bruch, in the Isis, 

 1823, 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 to a 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 (Mw/Zer'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 corpuscles (Die Pacinischen 

 Korperchen, 1844, p. 14, fig. 2).* 



* [ § 323, note 2.] Will (Schleiden and Fro- 

 riep''s Not. 1848, Aug. p. 145) has made chemico- 

 microscopical investigations upon the nature of this 

 peculiar poisoning power manifested in the proces- 

 sionary moths ; his researches were u))on Bombyx 

 processionea. The poisonous material was found 

 to be formic acid in a free and highly-concentrated 

 state ; it was met with in all i arts of the cater- 

 pillar, but especially in the faeces, in the greenish- 

 yellow liquid emitted by these animals when di- 



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. —Ed. 



I 



