$$ 322, 323. THE INSECTA. 401 
Siebold. Ueber die Fortpflanzung von Psyche: Ein Beitrag zur Natur- 
geschichte der Schmetterlinge—in Siedold and Klliker’s Zeitsch. I. 
1848, p. 93; see, also, for further researches on the subject, his Bericht tb. 
die entomol. Arbeiten d. schles. Gesellsch. in J. 1850, or its transl. in the 
Transact. of the Ent. Soc. I. 1851, p. 234. 
Leydig. Die Dotterfurchung nach ihrem Vorkommen in der Thierwelt 
und nach ihrer Bedeutung, in the Isis, 1848, Hft. 3. 
Hinige Bemerkungen iiber dei Eutwickelung der Blattlause, 
in Siebold and Killiker’s Zeitsch. 1850, II. p. 62. 
—— Anatomisches und Histologisches tiber die Larve von Corethra 
plumicornis, in Ibid, IIT. 1852, p, 435. 
Zur Anatomie von Coccus hesperidum, in Ibid. V. 1853, p. 1. 
Meyer. Ueber die Entwickelung des Fettkérpers, der. Tracheen und 
der Keimbereitenden Geschlechtstheile bei den Lepidopteren, in Siebold 
and K iliker’s Zeitsch. I. 1849, p. 175; see also the Mitth. d. naturf. Ges. 
in Zurich, Hft. 2, p. 206. 
See, also, the various writings referred to in my notes. — Ep. 
CHAPTER I. 
EXTERNAL ENVELOPE AND CUTANEOUS SKELETON, 
§ 822. 
The cutaneous envelope of the multi-articulate body of the Insecta con- 
sists, as with the other Arthropoda, of a kind of external skeleton, of a con- 
sistence sometimes leathery and soft, sometimes horny and solid. Its 
elasticity and flexibility is limited to the points of junction of the segments 
of the body, and of the articles of, the extremities. Its characteristic 
chemical substance is likewise chitine, a peculiar azotic matter insoluble in 
caustic potass, and with which highly-colored pigments are often chemically 
combined.” Chitine enters also into the composition gf the hairs and the 
scales of the skin, and the internal processes which may be regarded as an 
Internal Skeleton. 
"§ 823. 
Histologically, the cutaneous envelope is so variously and often so ex- 
1See Oder, Mém. de la Soc. d’Hist. Nat. de 
Paris, 1. loo. cit. ; Lassaigne, Compt. rend. XVI. 
1848, p. 1087, or Froriep’s neue Notiz. XX VII. p. 
7, and Schmidt, Zur vergleich. Physiol. &c. p. 
“82, Lassaigne has proposed for this substance 
the name Entomoderm. The coloration of the 
* [ § 322, note 1.] Recent researches have 
shown that the peculiar substance Chitine is not 
limited in its distribution to the Arthropoda, for it 
has been found in nearly every class of the Inver- 
tebrata. See Grube, Miiller’s Arch. 1848, p. 461, 
34* 
cutaneous skeleton is probably due to an oil 
with which the chitine is impregnated, especially . 
with the Coleoptera. 
See Bernard-Deschamps, Sur les Elytres des. 
Coléoptéres, in the Ann. d. Sc. Nat. ILI. 1845, p. 
354.* 
and Wiegmann’s Arch. 1850, p. 253 ; Schultze, 
Beitr. zur Naturgesch. d. Turbellarien, p. 33 5 and 
Leuckart, Morphol. der wirbellosen Thiere, p. 49, 
in Siebold and Kélliker’s Zeitsch. 1851, p. 192, 
and in Wiegmann’s Arch. 1852, p. 22. — Ep. 
