IV. INTRODUCTION. 



thoracio portion. The eyes, too, are all simple ; thus differing 

 remarkably from the compound eyes of the Insecta ; and the 

 legs (six in the insect tribes) are always eight in the spider. 



Differences Between Spiders and Other Arachnids. 



The different characters above detailed are easily observed, 

 and -will furnish a ready answer to tho question, " Spider or 

 insect ? " But as the various Orders of Arachnids — of which 

 the spiders constitute one Order only — share, with modifications, 

 in all those characters, one or two of the leading distinctions 

 must be mentioned, by which a spider may be known either 

 from the Acaridea — Mites — or the Phalangidea — Harvest-men — 

 or from a Pseudo-scorpion — Scorpionidea — which are the only 

 three Orders of Arachnids represented in Britain, besides 

 spiders — Araneidea, i.e., if we except the Pycnogonidea, marine 

 animals, whose position is still questionable. 



A spider can be distinguished at once from one of the Acaridea 

 (or Mite-tribes), by the latter possessing a body, which consists, 

 at first sight, of one portion only ; the outer skin being con- 

 tinuous, and, in many cases, not showing, by even a suture, or 

 groove, any division between the cephalo-thorax and abdomen. 



From the Phalangidea (or Harvest-men), a spider may be 

 recognised by the same general appearance in the former, as 

 that presented by an Acarid ; but although the body of a 

 Harvest-man appears at first sight to consist of one 

 portion only, the cephalo -thorax is, usually, distinctly 

 defined by a transverse indentation, or groove ; the abdomen 

 is covered by a series of coriaceous, or somewhat horny, 

 transverse folds, or plates ; the eyes are (in all European species) 

 two only, placed, one on each side of a tubercular eminence, 

 near the fore extremity of the cephalo-thorax ; and the legs are 

 generally very long, and of extraordinary slenderness ; the 

 terminal joint being sub-divided into numerous minuto articula- 

 tions. 



The Pseudo-scorpiones (or Chelifera), forming a sub-order 

 of the Scorpionidea, are a small group of minute, but curious 



