14 'THR STUDY OF INSECTS. 



Very great differences exist in the several orders of the 

 Arachnida in respect to the division of the body into seg- 

 ments. In arranging the orders in a series, we place first 

 those in which the segments of the body are most distinctly 

 indicated, while those which seem to depart more widely 

 from the segmented type characteristic of the Arthropoda 

 are placed later. 



The class Arachnida includes seven orders ; these are 

 designated as follows : 



The Scorpions, Order SCORPIONIDA (p. 15). 



The Jointed Spiders, Order SOLPUGIDA (p. 16). 



The Pseudoscorpions, Order PSEUDOSCORPIONES (p. 17). 



The Whip-scorpions, Order PEDIPALPI (p. 17). 



The Harvestmen, Order PHALANGIDEA(p. 19). 



The Spiders, Order ARANEIDA (p. 20). 



The Mites, Order ACARINA (p. 42). 



TABLE OF THE ORDERS OF THE ARACHNIDA. 



A. Abdomen distinctly segmented. 

 B. Abdomen with a tail-like prolongation. 



C. Tail stout and armed with a sting at the end ; first pair of legs 

 /iot greatly elongated ; a pair of comb-like appendages on the 

 lower side of the second abdominal segment in the adult. 



(Scorpions.} p. 15 SCORPIONIDA. 



CC. Tail slender, whip-lash like, without sting; first pair of legs 

 much longer than the others ; without comb-like appendages 

 on abdomen. (Whip-scorpions^) (Thelyphonidce.) p. 17. 



PEDIPALPI. 

 BB. Abdomen without a tail-like prolongation. 



C. Palpi with pincer-like claws. (Pseudoscorpions.') p. 17. 



PSEUDOSCORPIONES. 

 CC. Palpi without pincer-like claws. 



D. Abdomen joined to the thorax by a slender stalk; front 

 legs greatly elongated and with whip-lash-like tarsi. (Whip- 

 scorpions.') (P/irym'dce.) p. 17 PEDIPALPI. 



DD. Abdomen broadly joined to the thorax. 

 E. Legs usually very long and slender; thorax not dis- 

 tinctly divided into three segments. (Harvestmen!) p. 19. 



PHALANGIDEA. 



EE. Legs moderately long; head distinct from thorax ; thorax 

 distinctly divided into three segments, p. 16. SoLPUGIPA- 



