Ciliary Mechanisms 



65 



mouth (;;/). This is the 

 normal food collecting pro- 

 cess. 



But when much material 

 arrives on the gill, it not 

 only falls into the grooves, 

 but adheres to the surfaces 

 of the folds (/) as well. 

 Everywhere it seems to 

 stimulate a copious secretion 

 of mucus, and the whole 

 mass, both in the grooves 

 and on the folds, becomes 

 continuous. Now begins a 

 struggle between opposing 

 tracts. The material in the 

 grooves is pushed toward the 

 base and that on the folds 

 toward the free edge of the 

 gill, as at b. The tension on 

 the string of mucus becomes 

 so great that finally — and in- 

 variably — it is lifted up out 

 of the grooves and all is 

 borne to the edge of the gill 

 (c). Now, too, the whole 

 gill is responding to the 

 stimulus of a large quantity 

 of foreign matter on its sur- 

 face, by writhing and sway- 

 ing from side to side. 



If it is the inner gill that 

 has made this collection, 



Fig. 16. — Three folds of the 

 surface of the gill of the 

 scallop (Pecten irradians) 

 to illustrate automatic action 

 of cilia in bearing small 

 quantities of material to the 

 mouth on the tract marked 

 m, and large quantities away 

 from the mouth and to the 

 mantle wall from the edge of 

 the gill. 



