502 



THE INVERTEBRATA 



ctenidium towards its ventral edge. During the passage the particles 

 in the stream become entangled in mucus, and on reaching the edge 

 the string-like masses of food and mucus are directed by other cilia 



Fig. 368, Diagrams to show ciliary currents oiMytilus. 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 thefront end of the gill as they normally do in life. The vertical arrows repre- 

 sent 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 exha- 

 lant 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; mh.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 collector current runs along the groove 

 under the mantle edge to the pouch x. aa. anterior adductor muscle; by.7?i. 

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



along the edge in the direction of the mouth, travelling partly in the 

 ''food groove' \ When the labial palps are reached the collected 



