$$ 263, 264. 
THE CRUSTACEA, 
309 
‘by Ray Soc. London, 1850. In this work are embodied the results of his 
earlier researches published in the Trans. of the Berwick Nat. Club, &c. 
Darwin. A monograph of the sub-class Cirripedia with figures of all 
the species. 
Published by Ray Soc. London, 1851. This work is rich in 
anatomical details, many of which are new. 
Van Beneden. 
Ann, d. Se. Nat. XVI. p. 71.— Ep. 
Recherches sur quelques Crustacés inferieurs, in the 
CHAPTER lI. 
EXTERNAL ENVELOPE AND CUTANEOUS SKELETON. 
: § 263. 
The External envelope of the Crustacea is more or less solid, and has the 
form of a multi-articulated, cutaneous skeleton, sometimes of a leathery or 
horny consistence, but generally consists of a hard, calcareous shell, 
It has, consequently, no contractility, and participates in the movements 
of the body only in a passive manner, that is, by the interarticular soft 
skin, and by the antennal and foot-like processes. 
In this cutaneous skeleton, whether it is leathery, horny, or calcareous, 
there is a peculiar organic substance as its base. . 
This substance, which 
is found in the cutaneous skeleton of other Arthropoda also, has received 
the name of Chitine. It resembles cellulose of plants in its insolubility in 
caustic potass, but differs essentially from it in containing nitrogen.” 
§ 264. 
Nothing in general can be said as to the Histological composition of this 
cutaneous skeleton of the Crustacea, for it differs widely not only in the 
yarious orders and families, but even in the different parts of the body of 
Whether hard 
1 This Chitine which was formerly taken for a 
horny substance, was first discovered with the 
Insecta by Odier (Mém. d. 1. Soc. d’Hist. Nat. de 
Paris, I. 1823, p. 29). Latterly, it has been care- 
fully investigated by C. Schmidt (Zur vergleich. 
Physiol. d. wirbellos, Thiere, 1845, p. 82), who 
found, moreover, that the cutaneous skeleton of 
Crustacea has the same composition ag that of 
Insecta. 
the same species.” 
* [ § 264, note 1.] Of the results of Lavalle’s 
observations it may be well to add his concluding 
remarks ; after a minute description of each por- 
or soft, it is usually composed of 
1 We are indebted to Valentin for the re- 
searches, few as they are, which have hitherto 
been made on the internal structure of the skele- 
ton of Crustacea; see his Repertor. f. Anat. u. 
Physiol. I. 1836, p. 122. : 
Lavalle is about to publish microscopical re- 
searches on the structure of the cutaneous skeleton 
of the Decapoda; see Ann. d. Sc. Nat. 1847, p. 
520" 
tined to give the body its form and ‘volume, to 
serve as points of attach it to the | 
muscles, to furnish the instruments of prehension 
tion of the tegumentary apparatus, he : 
“T shall here only observe further, that my inves- 
tigations seem to be in complete opposition to the 
theories which make the shell of the Crustacea an- 
alogous (homologous) to the scaly epidermis of 
Serpents and Lizards. I see no analogy (ho- 
mology) between the shedding of the shell of the 
Crustacea, — which divests them of organs dés- 
and 3 organs placed not only on the 
surface of the body, but often immersed in the 
midst of soft parts, and in which we find an organ- 
{zation such as I have described, —and the peri-~ 
odical shedding observed in reptiles of a thin 
epidermis, without consistency, completely unor 
ganized and incapable of fulfilling any of the 
uses to which the shell is destined. My re- 
