324 



GOMPARATIVE ANATOMY 



CHAP. 



C. The Respiratory Organs — Gills. 



Eespiration always takes place in Crustaceans by means of the 

 outer integument. In small Crustaceans, in which the cuticle lying 

 over the hypodermis is thin and delicate, the whole body surface 



Fig. 225.— Pleopoda (abdominal feet) of Leptostraoa and Malaoostraoa. A, End of the 

 abdomen of Diastylis stygia (after G. O. Sars) ; V, VI, VII, abdominal segments ; VII, telson ; p^, 

 pleopoda of the 6th segment ; en, endopodite ; ex, exopodite. B, 2d pleopod with gills, exo- and 

 endo-podite of Siilella Thompsonii (after G. O. Sars). C, End of the abdomen (caudal fin) of Siri- 

 ella gracilis (after G. O. Sars) ; VI, 6th abdominal segment ; VII, 7th abdominal segment (telson) ; 

 en, ex, endo- and exo-podites of the 6th pleopoda, which together with the telson form the caudal 

 fin ; g, auditory organ. D, An anterior pleopod of Nebalia (after Glaus) ; ex, exopodite ; en, 

 endopodite. E, Nebalia, 6th pleopod of the J (after Glaus). F, Anilocra (Isopod), caudal fln ; VI, 

 6th abdominal segment ; VII, telson ; pq, 6th pleopod with exopodite (ex) and endopodite (en) (after 

 Delage). G, Lyslanassa producta (AmijM2J0d) ; end of the abdomen with the 4th, 6th, and 6th 

 pleopoda, jjj, Ps, pe ; I^i ^t ^'I< ^II< abdominal segments ; en, endo-, ex, exo-podite (after Goes). 

 H, Diastylis stygia, 1st pair of pleopoda ; ex, exo-, en, endo-podite (after G. 0. Sars). I-N, 

 Astacus fluviatllls. I, 3d pleopod of male ; K, 1st pleopod of female ; L, 1st pleopod of male ^ 

 M, 3d pleopod of the female ; N, 2d pleopod of the male. 1, Anterior surface ; 2, posterior 

 surface ; ex, exopodite ; a, the roUed-up plate of the endopodite ; &, jointed end of the endopodite 

 (after Huxley). 



breathes. This is especially the case in Ostracoda, Copepoda, many 



Cladocera, and many Girripedia, which have no specific respiratory organs. 



In the great majority of Crustaceans, however, the respiration 



is particularly active at definite parts of the body, even if in addi- 



