272 MOLLUSCA. 
On either side of the foot there hang the gzd/-damella, or 
ctentdia. These are lamellze on each side, formed in each 
case by a gi//-plate folded on itself, the outer 
gill-plate outwards and the inner inwards. The 
gill-plates are themselves composed of a number of gi//- 
Jfilaments, which hang perpendicularly in a single row from 
a horizontal axis which is fused with the body-wall. 
Respiratory. 
Fig. 191 VIEW oF ANODONTA WITH LEFT MANTLE-FLAP THROWN 
Back. (Ad nat.) 
_ Left Mantle Flap. 
Outer Gill. 
Inner Gill. 
Anterior Adductor. 
Exhalent 
Chamber. 
Inhalent 
Aperture. 
Outer Gill. 
Renal Inner Gill. 
Foot. Labial Genital Aperture. 
f Palp. Aperture. 
A ctenidium therefore consists of a medium axis with 
two rows of gill-filaments, each row forming a gill-plate. In 
Anodonta. but not in all Lamellibranchiata, these gill-plates 
are bent double to form in each case two gill-lamellz. In 
addition, the filaments and the gill-lamelle have fused with 
their fellows and thus form a network of filaments. The 
whole are ciliated and cause currents of water and food- 
particles to pass into the mantle-cavity by the inhalent 
aperture. . The free edges of the upturned gill-plates are 
fused to the body-wall, and thus shut off outer and inner 
