264 



CLASSIFICATION OF ANIMALS 



566. Class HI. Arachnoidea. The Arachnoidea are air- 

 breathing Arthropods, with a cephalothorax, two pairs of 

 mouth appendages and four pairs of locomotor appendages. 

 The abdomen has no appendages. There are from 2 to 1 2 eyes. 



567. Order i. The Scorpionidea 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 chelicerae 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 



