LAM ELL IB RANG HI AT A 



577 



movement it is thus seen that they feed in the manner of a sedentary 

 organism, and it is not surprising that there are many fixed and 

 burrowing forms among them. 



inh.s. 



Fig. 393. Diagrams to show ciliary currents of Mytilus. Adapted from Orton. 



A, Food currents with left lobe of mantle removed to show the outer lamella 

 only of the left gill, and the two palps of the left side separated and not embrac- 

 ing the front end of the gill as they normally do in life. The vertical arrows re- 

 present the currents caused by the frontal cilia, those at the bottom of the gill 

 the main food current running to the mouth and that at the top of the gill the 

 exhalant current, x. represents a curtain which prevents the inhalant current 

 from directly impinging on the surface of the gill, an opportunity being thus 

 afforded for a preliminary rejection of particles, by. byssus threads ; ct. outer 

 lamella of left ctenidium ; exh.c. course of exhalant current shown by arrows 

 in the epibranchial chamber, the roof of which is indicated by dots ; F. foot ; 

 inh.s. left lip of inhalant siphon ; inh.c. inhalant current ; M. mouth ; pp. palps. 



B, Rejection currents. Mytilus with foot and the gills removed so as to show 

 the interior of the right lobe of the mantle. The direction of the currents 

 caused by the cilia is shown by arrows. The palps of the left side and the 

 anterior end of the outer left gill remain and the rejection current marked by 

 three parallel arrows is shown. The colleQtor current runs along the groove 

 under the mantle edge to the pouch x. aa. anterior adductor muscle ; by.m. 

 muscles of the byssus ; pa. posterior adductor muscle. Other letters as above. 



A short oesophagus leads directly into the stomach, which is a wide 

 sac receiving on each side the ducts of the digestive gland which is 



