IX] 



THE RESPIRATORY SYSTEM 



197 



Structure and Histology of the Caudal Gills (fig. 86). 



The Triquetral Gill possesses a thick cuticle, considerably 

 swollen along the mid-rib. Beneath this lies a layer of pigmented 

 hypoderm cells. In the interior of the gill there are two main 

 longitudinal tracheae, with a number of obliquely-placed branches. 

 There are also two main longitudinal blood-channels, one dorsal 

 (efferent), the other ventral (afferent) ; these become confluent 



A. 



Fig. 86. Histology of the caudal gill. A. T.S. through basal third of saccus of 

 Diphlebia lestoldes Selys ( x 47). B. Small portion of same ( x 200). c. T.S. 

 through basal third of lateral lamellar gill of Syrdestes weyersi Selys ( x 47). 

 D. Small portion of same ( x 200). al alveoli; b blood-plasma; CM cuticle; 

 h haemocoele; hy hypoderm; nu nucleus of alveolus; tr main longitudinal 

 trachea; tr' branch trachea. Original. 



