CILIARY MECHANISMS ON THE GILL IN AMPHIOXUS. 35 



rapidly. Perhaps the function of these cilia may be detected by 

 examining their action through a microscope in the whole living and 

 feeding animal, and an attempt will be made to find an animal in which 

 this is possible. It is probable that they assist in passing mucus on to 

 the walls of the pharynx, as has been suggested for the similar cilia in 

 Amphioxus. 



Examination of the peri-pharyngeal bands through a microscope shows 

 that the cilia in these grooves lash from the endostyle towards the dorsal 

 lamina. These grooves serve to collect and transport to the dorsal 

 lamina such particles as fall out of the main stream at the entrance to the 

 pharynx. 



COMPAEISON OF THE MODE OF FEEDING IN 

 AMPHIOXUS AND ASCIDIANS. 

 From the foregoing description it will be seen that there is an exact 

 correspondence in the mode of feeding in Amphioxus and Ascidians. 

 In these animals the lateral cilia on the gill- bars are the main factors in 

 producing the main current ; mucus is passed on to the gill-bars by the 

 outer tracts of cilia on the endostyle, and food-particles are collected and 

 transported to the dorsal region of the gill by the pharyngeal or frontal 

 cilia on the gill-bars. The food collected in the dorsal wall of the pharynx 

 is transported backwards, to be passed into the digestive tract. Thus 

 the diagram of the ciliary mechanism on the gill of Amphioxus (see Fig. 6) 

 will serve equally well for Ascidians in general. The cilia in the peri- 

 pharyngeal bands in both of these groups of animals lash from the 

 endostyle towards the dorsal groove, and collect and transport to the 

 dorsal groove those particles which fall out of the main stream at 

 the entrance to the pharynx. The process of feeding in both Amphioxus 

 and Ascidians is automatic, but at the same time these animils are 

 able to select from the food-stream the finer food-particles by means of 

 their buccal tentacles. Ascidians, moreover, have been observed to 

 reject food after it has been collected in masses on the gill by suddenly 

 contracting the walls of the pharynx and expeUing the whole mass. It is 

 also not improbable that the pharyngocloacal slits observed by Garstang 

 in Ascidians (18, p. 132), may be exits from the pharynx used for 

 relieving that organ when overburdened with undesirable matter. 

 On the other hand Amphioxus is obliged to ingest all that passes 

 beyond the oral aperture. 



