\. Nucula. 



GILLS OF LAMELLIBRANCHIATA 



Ctenidium with two rows of short filaments. 



2. Mytilus. (a) Adjacent filaments of the gill mounted in sea-water ciliary junctions. Only 

 one of the limbs of the filaments should be mounted. 



(b} Single filament seen endwise. Ascending limb ; descending limb ; interlamellar concrescences. 



