SUPPLEMENT 



CLASS ARACHNIDA*. 



The animals of this class, though approximating to the 

 insects, and though always considered as such in popular 

 language, differ from them, as may be seen in the text, by 

 certain marked characters which it is unnecessary to repeat 

 here. They were first separated under the above denomina- 

 tion by M. de Lamarck. He, however, comprehends in this 

 class all the apterous insects of Linnaeus, with the exception 

 of the genera cancer, tnonocuhis, oniscus, which compose his 

 class of the Crustacea, and those of termes and judex, which 

 he reunites to the insects properly so called. 



The Arachnida, thus named from the principal and most 

 numerous genus, that of the spiders, {cirachne in Greek) have 

 at the external surface of the body apertures for the admission 

 of air, or stigmata, in this respect approaching the insects, 

 and departing from the Crustacea. But they have not, like 

 the first, antennas and a distinct head. Their mandibles, or 

 rather the pieces which replace them, are contiguous and 

 advanced parallel to one another, in the direction of the length 

 of the body ; the jaws, or the parts analogous thereto, are but an 

 expansion of the first articulation of the haunches of the an- 



* We adopt the word Arachnida in the Supplement as the term most 

 used by English naturahsts, though it will be observed that the equivalent 

 Arachnides is the word made use of in the text. — Ed. 



