ARTHROPODA. 135 



Order 5. Phalangida. 



Body short and oval. Abdomen composed of 

 six segments. Chelicerae chelate. Pedipalpi 

 and legs very long and slender. Respiration by 

 tracheae. (Phalangium.) 



Order 6. Araneida. 



Abdomen unsegmented and usually distinct. 

 Chelicerae end in claws that are provided with 

 poison glands. Lung-books and sometimes tra- 

 cheae also are present. Spinnerets present on the 

 abdomen. (Epeira, Agalena.) 



Order 7. Acarida. 



Body not divided into regions. Biting or pierc- 

 ing and sucking mouth-parts. Respiration by 

 tracheae or through integument. (Sarcoptes, 

 Dermacentor.) 

 Supplementary to the Arachnoidea. 



Pycnogonida. 



(Doubtfully referred to the group.) Body com- 

 posed of segmented cephalothorax and vestigial 

 abdomen. Legs very long, angular, and con- 

 taining portions of the viscera. No special 

 respiratory organs. (Phoxichilidium.) 

 CLASS 3. Onychophora. 



Elongated bodies with some annelid-like charac- 

 ters. Appendages short, numerous, and creased 

 rather than jointed. Respiration by means of 

 tracheae. (Peripatus.) 

 CLASS 4. Myriapoda. 



Generally elongated bodies with numerous 

 jointed appendages. A distinct head bearing 

 ocelli, antennae, and jaws is present. Respira- 

 tion by means of tracheae. 



Order 1. Symphyla. 



With not more than twelve leg-bearing trunk 

 segments. A single pair of branching tracheae. 

 (Scolopendrella.) 



Order 2. Chilopoda. 



With numerous trunk segments, each with a sin- 

 gle pair of legs. First pair of trunk appendages 

 forming poison jaws. Body dorso-ventrally com- 

 pressed. (Lithobius.) 



