CILIARY MECHANISMS ON THE GILL IN AMPHIOXUS. 4T 



is doubtless the same as in the Plymouth Amphioxus. He j^ivos the 

 impression, however, that this is the main method of feeding, but such 

 is not the case, as will have been seen fiom the foregoing description. 



SUMMAKY. 



The mode of feeding in Amphioxus is effected by — 



(1) The maintenance of a stream of water through the pharynx by 



rows of lateral cilia on the gill-bars. 



(2) The throwing out of mucus from the endostyle on to the gill-bars 



to serve for entrapping food-particles. 



(3) The collection of food-particles by rows of cilia on the pharyngeal 



surface of the gill-bars ; these cilia work up the food- 

 particles with mucus into cylindrical masses and transport 

 such masses dorsally into the dorsal groove which carries 

 the collected masses backwards into the digestive tract. 



Thus the ciliary mechanisms on a gill-bar of Amphioxus are exactly 

 the same as those on the gill-filaments of some Lamellibranchs, as Pecten,. 

 and some Gastropods, as Crepidula. 



A subsidiary mode of food-collection is effected in the buccal cavity 

 of Amphioxus by the ciliated tract known as the wheel organ, and 

 Hatchek's pit, which supplies mucus for entrapping food-particles. 

 These particles are passed on to the peri-pharyngeal bands which 

 conduct them in turn into the dorsal groove. 



The gill of Amphioxus functions mainly as a feeding organ and a w^ater 

 pump, and probably not at all as an organ for aerating the blood. 



The mode of feeding in Ascidians is almost exactly the same as that 

 described above for Amphioxus. Food-collection, however, in Ascidians 

 is effected by cilia on the papillse and similar outgrowths on the gill, 

 and is also helped in some forms by transverse waving of the 

 longitudinal bars, by which process the food is pushed as well as 

 lashed towards the dorsal region of the pharynx. 



The observations here made lend support to the view that the neural 

 gland in Ascidians is an organ for secreting mucus, which aids in the 

 capture and transportation of food-particles, and that the dorsal tubercle 

 of Ascidians is an organ for passing mucus on to the pharynx ; the 

 corresponding structures in Amphioxus, namely, Hatchek's pit and the 

 wheel organ, are here shown to effect food-collection in the buccal cavity. 



The cavity in the body of Ascidians through which the food stream 



