159 



CLASS II. 



ARACHNIDES. 



The Arachnides, which compose the second class of articu- 

 lated animals provided with movable feet, are, as well as the 

 Crustacea, deprived of wings, are not subject to changes of 

 form or do not experience 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 excepted : but they 

 differ from them as well as from Insects in several particulars. 

 Like the latter, the surface of their body presents apertures 

 or transverse fissures called stigmata(l), 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 functions of lungs, that are contained in sacs of 

 which these stigmata are the apertures, or by radiated tra- 

 cheae(2). The visual organs merely consist of ocelli, which, 

 when numerous, are variously grouped. The head-, usually 

 confounded with the thorax, in place of the antennse, has 

 two articulated pieces in the form of small didactyle or mo* 

 nodactyle 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 business of manducation, and replaced in 



(1) A vague and improper appellation, for which we might substitute pneumos- 

 toma, air-mouth, or spiraculum. 



(2) See general observations on Insects. 



