CLASS II. 
AR.ACHNIDES. 
The Arachnides, which compose the second class of articulated 
animals provided with moveable feet, are, as well as the Crustacea, 
deprived of wings, are not subject to changes of form, or do not ex- 
perience any metamorphosis, simply casting their skin. Their sexual 
organs also ai’e at a distance from the posterior extremity of the body, 
and situated at the base of the abdomen, those of several males ex- 
cepted ; but they differ from them as well as from Insects in several 
particulars. Like the latter, the surface of their body presents aper- 
tures or transverse fissures called stigmata,* for the introduction of air, 
but they are few in number — eight at most, and usually but two — and 
confined to the inferior portion of the abdomen. Respiration is also 
effected either by means of air-branchiae, fulfilling the function of 
lungs, that are contained in sacs of which these stigmata are the 
apertures, or by radiated tracheaef. The visual organs merely con- 
sist of ocelli, which, when numerous, are variously grouped. The 
head, usually confounded with the thorax, in place of the antennae 
has two articulated pieces in the form of small didactyle or monodac- 
tyle chelae, improperly compared to the mandibles of Insects, and so 
denominated, moving in a contrary direction to the former, or from 
above downwards, still however co-operating in the manducation, 
and replaced in the Arachnides, Avhere the mouth has the form of a 
siphon or sucker, by two pointed blades which act as lancets^. A 
kind of lip — labium. Fab. — or rather ligula, produced by a pectoral 
prolongation; two jaws formed by the radical joint of the first seg- 
* A vague and improper appellation, for which we might substitute pnmmostuma, 
— air-mouth, — or spiracuhtm. 
■f- See general observations on Insects. 
+ Chelicera, or forceps-ant cnna ; the evident result of the comparison between 
them and the intermediate antennae of various Crustacea, those of the Paecilcpoda 
particularly. It cannot then be said, strictly speaking, that the Arachnides are 
deprived of antennae, a negative character, which, previous to us, had been exclu- 
sively attributed to them. 
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