2 74 



MANUAL OF ZOOLOGY 



cavity, and out at the exhalant siphon. The ingoing cur- 

 rent carries with it not only oxygen for the aeration of the 



A 



y r ° 9 



b. 



i.lj 



^mtm^vm 





Fig. 163. — 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. v, blood-vessels; c/i, chitin; f, branchial filaments; e/>, epithelium; 

 z'.f.j, inter-filamental junction ; z. I, inner lamella; i. I. J, inter-lamellar junction; 

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

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



blood, but also diatoms, Infusoria, and other microscopic 

 organisms, which are swept into the mouth by the cilia cov- 



