INTRODUCTION. 



Branch ARTICULATA. 



Class I. | Anndidcs or Anarthropoda. 



Condylopoda or 

 Arthropoda. 



Subclass : I. Insects. II. Myriapoda. III. ARACHNIDA. IV. Crustacea. 



Orders ; i. Acaridea. ii. Pycnogonidca. iii. Fhalangidea. iv. Solpugidea. 

 v. Scorpionidea. vi. Thelyphonidea. vii. ARANEIDEA. 



Araohnida. — Not subject to metamorphosis, but developed by 

 successive moultings of the skin. Organs of locomotion, 

 eight. Body, in general, divided into two principal parts, 

 Cephalo-thorax and Abdomen; in some groups the abdomen is 

 divided into more or less distinct segments, but in such cases no 

 organs of locomotion are ever attached to them. Respiration 

 (where distinct organs exist) is either tracheal, sac-trachea!, or 

 the two co-existent. 



Coming now at once to the order Araneidea, we have the two 

 parts of the body, CcpJialo-thorax and Abdomen, always quite 

 distinct from each other. The former, by its converging 

 lateral indentations, shows unmistakeable traces of pristine 

 segmentation ; the latter, occasionally showing the same by 

 transverse folds in the integment near the posterior extremity ; 

 excepting in these respects the cuticle of both is continuous. 

 Palpi, in males, used in copulation ; and especially developed, at 

 their terminal joint, for that purpose; in females tho palpi are 

 simple, and generally terminate with a single claw. Legs always 

 furnished with two, or three, terminal tarsal claws. Respiration, 

 both tracheal and sac-tracheal. 



By the above characters spiders are at once separated from all 

 other Arachnids, as well as from Insects, Myriapods, and Crusta- 

 ceans. 



