28 J. H. ORTON. 



The main cilia which collect and transport the food-particles are those 

 on the pharyngeal surface of the gill-filaments, namely, the frontal cilia 

 (see Figs. 4 and 6, f.c, and Fig. 3). These cilia lash in a direction which is 

 chiefly along the length of the bars, but actually at an angle to the bars 

 in a ventro-dorsal direction (see the arrows on the right side of Fig. 3). 

 The gill-bars, it is to be remembered, run in the living animal in an antero- 

 dorsal to postero-ventral course, as is shown in Figs. 1, 2, and 3. Food- 

 collection is effected in the following manner. Mucus is secreted by the- 

 endostyle and passed on to the gill-bars in a thin sheet by the cilia on the 

 lateral portions of the endostyle. Probably mucus is secreted also by the 

 pharyngeal epithelium of the gill-bars. Food-particles are drawn against 

 the gill-filaments by the lateral cilia on those filaments, as we have already 

 seen ; the particles become entangled in the mucus in which they are 

 hurried along the face of the gill-bars into the dorsal groove by the 

 frontal or pharyngeal cilia. The actions of these different mechanisms 

 are depicted in the accompanying diagram, Fig. 6. 



It is thus evident that feeding in Amphioxus occurs automatically as 

 in the Lamellibranchs. Amphioxus, however, has an advantage over 

 most Lamellibranchs in being able to swim away from a region where 

 the water is laden with innutritions or undesirable particles. And, 

 indeed, the occurrence of Amphioxus mainly on shelly or gravelly 

 grounds may be due largely to the desire .of the animal to seek out 

 grounds where the water is relatively free from undesirable, i.e. 

 innutritiors particles. 



A food-collection of minor importance is also effected, as we have seen, 

 in the buccal cavity. Food-particles are collected into the ciliated grooves 

 on the wall of this cavity and transported in mucus through the mouth 

 to the peri-pharyngeal bands, often, however, these particles are drawn 

 into the pharynx in the main stream at the oral aperture. 



These ciliated grooves in the buccal cavity doubtless lend some small 

 aid to the lateral cilia of the gill-filaments in producing the main current, 

 as probably also do the ab-frontal cilia of the filaments. Short cilia have 

 also been observed on the atrial epithelium overlying the gonads. 

 These cilia lash ventrally, and thus help somewhat in producing the 

 main current. 



THE FUNCTION OF THE PHAKYNX IN AMPHIOXUS. 



It is generally stated that the gill of Amphioxus functions mainly as a 

 respiratory and only secondarily as a feeding organ. In the light of the 

 present researches, however, it would appear that the pharynx functions 



