XI 



PHYLUM MOLLUSCA 



273 



which sets in through the inhalant siphon into the pallial 

 cavity, and out at the exhalant siphon. The in-going 



FIG. 151. Anodonta cygnea. A, transverse section of outer ; B, of inner gill; 

 C, diagram of gill-structure ; D, transverse section of gill filament, b. c. blood- 

 corpuscle ; b. 7'. blood-vessels ; ch. chitin ; f. branchial filaments ; ep. epithelium ; 

 i.f.j. inter-filamental junction ; /. /. inner lamella ; /. /./. inter-lamellar junction ; 

 o. 1. outer lamella ; os. external ostium ; os'. internal ostium ; r. chitinous rods ; 

 iv. t. water tubes. (A, B, and D, after Peck.) 



current carries with it not only oxygen for the aeration of 

 the blood, but also Diatoms, Infusoria, and other micro- 

 Man. Zool, 



