CR VST A GE A— GILLS 



323 



of the anterior pleopoda contain air chambers. In the Anisopoda the pleopoda are 

 biramose 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, 

 each of whose outer lamellis carries a branched gill. The 6th pair of pleopoda form 

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



In the Ciimacea the 6th pair of pleopoda {A, p^) 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 {S), and either present in their full 

 numbers or in 2 to 3 pairs. 



In the Schizopoda the 6th pair of pleopoda (C) forms mth 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 



Fio. 224. Thoracic fast of Astaous fluvlatilis (after Huxley). A, 2<1 thoracic foot (2d maxil- 



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

 showing an ambulatory foot and gills. D, 3d thoracic foot (3d maxillipede). I, 11, Joints of 

 the protopodite ; 1-5, of the endopodite eji ; ex, exopodite ; poi, podobranchias ; ab, arthrobranchise ; 

 plb, pleurobranchlEe ; k, masticatory ridge. 



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

 the male of Siriella the pleopoda carry gills {B). 



Deaapoda (I-N). — The development of the pleopoda stands in direct relation to 

 the development of the abdomen itself. In the long-tailed Decapoda [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 Brachyura the pleopoda, in correspondence mth 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 Decapodan male as copulatory organs. In the female the pleopoda often carry 

 the eggs after their discharge and fertilisation. 



