CRUSTACEA GILLS 



323 



of the anterior pleopoda contain air chambers. In the Anisojmla the pleopoda an- 

 birumusc swimming feet, not serving for respiration. 



Thoracostraca. In the Stomatopoda we find on the strong abdomen 6 pairs of 

 well-developed typical biramose pleopoda. The 5 anterior pairs are swimming feet, 

 eacli of whose outer lamella? carries a branched gill. The 6th pair of pleopoda form 

 with the telson (7th abdominal segment) a strong caudal fin. 



In the Cumacea the 6th pair of pleopoda (A, _?? 6 ) consists of long bifurcated 

 processes. The pleopoda of the 5 anterior abdominal segments are wanting in the 

 female ; in the male they are swimming feet (H], and either present in their full 

 numbers or in 2 to 3 pairs. 



In the Schizopoda the 6th pair of pleopoda (C) forms with the telson a caudal fin. 

 Where there is an auditory organ it lies on the inner lamella of this pleopod. The 

 5 anterior pairs of pleopoda are well-developed biramose swimming feet, in the male 



D 



FIG. 224. Thoracic feet of Astacus fluviatilis (after Huxley). .4, 2d thoracic foot (2d maxil- 

 lipede). B, 1st thoracic foot (1st maxillipede). C, Part of transverse section through the thorax, 

 showing an ambulatory foot and gills. D, 3d thoracic foot (3d maxillipede). /, II, Joints of 

 the protopodite ; 1-5, of the endopodite en ; ex, exopodite ; pob, podobranchire ; &, arthrobranchia? ; 

 plb, pleurobrauchife ; k, masticatory ridge. 



at least. The 2 anterior pairs serve as copulatory organs in the Euphausidce. In 

 the male of Siriella the pleopoda carry gills (). 



Dccapoda (1-N}. The development of the pleopoda stands in direct relation to 

 the development of the abdomen itself. In the long-tailed Dccapoda (Macrura) 6 

 pairs of biramose pleopoda are generally found. The 6th pair with the telson forms 

 a strong caudal fin. The 5 anterior pairs play no very important part in locomotion. 

 In the Bracliyura the pleopoda, in correspondence with the great reduction of the 

 abdomen, are reduced. A caudal fin is usually wanting. In the male only the 2 

 anterior pairs of pleopoda are found, in the female 4 pairs. The caudal fin is 

 generally reduced in the Anomura, and the pleopoda are truncated and only 

 developed on one side. The 2 anterior pairs of pleopoda very generally serve in 

 the Dccapodan male as copulatory organs. In the female the pleopoda often carry 

 the eggs after their discharge and fertilisation. 



