CLASSIFICATION OF CRUSTACEA 



351 



respiratory tubes in the abdominal limbs, and corresponding forms on 

 the shore {e.g. Ligia, Idotea) ; the Amphipods, with lateral flattening 



ABD 



Fig. 196. — Dorsal view of a wood-louse {Oniscus), a typical Isopod, 

 but of terrestrial habits— after Webb and Sillem. The abdominal 

 appendages or pleopods are penetrated by minute air-containing 

 tubes which form a respiratory system adapted for terrestrial con- 

 ditions. In the marine Isopods, the endopodites of the abdominal 

 appendages are gill-like and serve for aquatic respiration. The 

 number of segments and appendages is like that in the crayfish. 



H., Head. 

 ABD., A segment of the abdomen. 



A., Antenna. 

 TH., A segment of the thorax. 

 A. P., Last pair of abdominal appendages. 



of the body, an anterior heart, and respiratory organs usually on the 

 thoracic limbs, e.g. Gammarus locusta in the shore pools, G. pulex in 



