CLASS II. 



ARACHNIDES. 



The Araclinides, 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 are 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 pneumosloma, 

 — air-mouth, — or sinraculum. 



f See general observations on Insects, 



X Chelicerte, ox forceps-antenna ; the evident result of the comparison between 

 them and the intermediate antennae of various Crustacea, those of the Paecilopoda 

 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. 



T 2 



