210 



THE CRAYFISH. PHYLUM ARTHROPODA 



TABLE II 



Ep=epipodite without a gill. 



R=abortive rudiment. 



(a)>t. 



as podobranchicE. Others stand upon the membranes which join 

 the hmbs to the body, and are known as arthrobranchiae, and a 



few stand upon the inner wall of 

 the gill-chamber (the side wall of 

 the thorax) above the legs, and are 

 known as pleurobranchiae, the three 

 names being often anghcised by omission 

 of the terminations. The distribution of 

 the gills is shown in Table II. 



Each arthrobranch and pleurobranch 

 has a tree-like structure, consisting of a 

 trunk or axis arising from the body by 

 one end, with numerous short branches 

 or filaments. In the podobranch the axis 

 is fused to the epipodite along the 

 greater part of its length, so that the 

 filaments appear to arise from the 

 epipodite. The tip of the gill, however, 

 stands free. The epipodite is folded 

 along its length, so that a groove is 

 formed, into which fits the gill of the limb next behind. 



oase 



Fig. 142. — A podobranch 

 of the crayfish, seen 

 from behind. 



base ; cp., coxopodite ; gill ; lam., 

 lamina ; sb., setobranch or 

 tuft of coxopoditic setae ; 

 stm., stem. 



OSMOTIC REGULATION AND EXCRETION 



In the head is a pair of coelomoducts (p. 189) called antennary 

 or green glands, situated immediately behind the antennae, upon 

 who^e basal joints they open. Each consists (Fig. 143) of a 



