CHARACTERISTICS OF INSECTS AND THEIR RELA TIVES 3 



IV. DEGENERATE ARTHROPODS OF DOUBTFUL POSITION 



Class Pycnogonida, page lo 

 Class Tardigrada, page 12 

 Class Pentastomida, page 14 



V. THE PRIMARILY AERIAL SERIES 



Class Onychophora (See above) 

 Class Diplopoda, page 15 

 Class Pauropoda, page 18 

 Class Chilopoda, page 20 

 Class Symphyla, page 23 

 Class Myrientomata, page 24 

 Class Hexapoda, page 26 



TABLE OF CLASSES OF THE ARTHROPODA 



A. Worm-like animals, with an unsegmented body, but with many 



unjointed legs Onychophora 



AA. Body more or less distinctly segmented except in a few degen- 

 erate forms. 

 B. With two pairs of antennae and at least five pairs of legs; 



respiration aquatic Crustacea 



BB. Without or apparently without antennae. 



C. With well-developed aquatic respiratory organs. 



Pal^ostracha 

 CC. With well-developed aerial respiratory organs or with- 

 out distinct respiratory organs. 

 D. With well-developed aerial respiratory organs. 



E. Body not resembling that of the Thysanura in form. 



Arachnida^ 

 EE. Body resembling that of the Thysanura in form 



(Family Eosentomidae) Myrientomata 



DD. Without distinct respiratory organs. 

 E. With distinctly segmented legs. 

 F. Body resembling that of the Thysanura in form, but 

 without antennae, and with three pairs of thoracic 

 legs and three pairs of vestigial abdominal legs 



(Family Acerentomidas) Myrientomata 



FF. With four or five pairs of ambulatory legs; 



abdomen vestigial Pycnogonida 



EE. Legs not distinctly segmented. 



F. With four pairs of legs in the adult instar. 



Tardigrada 



