264 



CLASSIFICATION OF ANIMALS 



566. Class III. Arachnoidea. — The Arachnoidea are air- 

 breathing Arthropods, with a cephalothorax, two pairs of 

 mouth appenchiges and four pairs of locomotor appendages. 

 The abdomen has no appendages. There are from 2 to 12 eyes. 



567. Order I. — The Scorpionidca are large Arachnoidea with a long 

 segmented abdomen consisting of a preabdomen of seven segments and 



Fig. 152. — A Scorpion, Buthus afer. X 1/2. 



a postabdomen of six segments and ending in a spine and poison gland. 

 The first and second pairs of appendages, the cheb'cera^ and maxillary- 

 palps are chelate. The respiratory organs consist of four pairs of book 

 lungs which open on the ventral side of the preabdomen. 



568. Order 2. — The Pedipalpi have clawed chelicerae, clawed or chelate 



