284 CLASS VIII. 
may be looked on as the rudiments of a neural skeleton. There is 
in each division of the thorax a process, which often has the form of 
the letter Y, supports the nervous cord, and by the expansion of 
its two branches, which are directed upwards, partly covers it. 
To this process AUDOUIN has given the name of Hntothorax ; it is 
even found in the head and sometimes in the first abdominal ring. 
These are the same processes which TREVIRANUS had already com- 
pared to vertebre'. These vertebre, however, are not joined 
together to form a spine, but are separated from each other by 
certain spaces. The dermal skeleton of Insects consists of a pecu- 
liar substance to which OpiER gave the name of Chitine, LASSAIGNE 
that of Entomoline*, which occurs also in the integument of Arach- 
noidea and Orustacea, and which is not soluble in caustic potass, 
neither is rendered yellow by nitric acid, like corneous tissue. It 
burns without fusion or intumescence. It forms different layers of 
which the most external is composed of irregular cells*. | 
The arrangement of the muscles is different in the different 
orders of Insects, nay, in the same insect in its different states, if it 
undergoes complete metamorphosis. The difference between the 
muscles of the thorax and of the abdomen, which in the per- 
fect insect*is so marked, is absent in the vermiform elongated 
larva, for instance, in caterpillars. Along the dorsal and ventral 
surface riband-like muscles run longitudinally ; there are different 
oblique muscles in addition. The muscles present in their bundles 
transverse stripes, as in vertebrate animals’. They are usually 
. 
skeleton ; see especially his excellent work Von den Ur-Theilen des Knochen- und Scha- 
len-Geriistes, Leipzig, 1826, folio. 
1 Verm. Schriften, IV. 8. 229, 230. 
2 See OpieR, Mem. de la Soc. d’ Hist. Nat. de Paris, 1. 1823, pp. 29—42, and the 
later investigations of C. Scumipr, Zur vergleichenden Physiologie der Thiere, Braun- 
schweig, 8vo. 8. 32, 52. 
3 Comp. H. Frey and R. Lruckarr in the new edition of R. Wagner, Lehrb. der 
Zootomie, revised by them, 1845, pp. 3—5; also H. Mayer in MUELLER’s Archiv, 
1842,s.12—16. In the skin of the Silkworms and their pupz (and also in other pup 
of lepidoptera) there are found stellate cells, which PLATTNER compares with the bone- 
corpuscles in the osseous tissues of vertebrates, MUELLER’S Archiv, 1844, 8. 46, 47. 
4 Since in every ring of the Larva’s body the same arrangement of the muscles is 
observable, the number of the muscles, when those of all the rings are counted together, 
is very great. LyonNnrET found in the larva of the Willow-hawk more than 4,000 
muscles. 
