CILIAKY MECHANISMS ON THE GILL IN AMPHIOXUS. 27 



mass with mucus on the way. A large number of these minor food-masses, 

 however, are swept into the main stream as they approach the oral 

 aperture and pass onwards into the pharynx. Some particles, however, 

 appear to pass between and sometimes along the velar tentacles on to the 

 internal surface of the pharynx, whence they are passed on to the peri- 

 pharyngeal grooves. It is well known that there are no gill openings 

 anterior to the peri-pharyngeal grooves. Thus the part of the pharynx 

 •anterior to the peri-pharyngeal grooves serves as a collecting ground for the 

 food-particles which have been caught in the buccal cavity. Most of the 

 particles, however, appear to pass around the ventral part of the mouth 

 to the peri-pharyngeal groove ; while others appear to pass dorsally 

 straight into the dorsal groove. There is also, however, a steady dribble 

 •of particles into the peri-pharyngeal groove from a position immediately 

 ventral to it. These particles are probably collected from the extreme 

 anterior portion of the endostyle, by which they are ejected in the same 

 way as we have seen at other parts. Doubtless these minor streams have 

 been the cause of the erroneous views which are current on the mode of 

 feeding in Amphioxus. If a little methylene blue is added to the water 

 from which an Amphioxus is feeding the edges of the ciliated paths in 

 the buccal cavity stain blue, which doubtless indicates the presence of 

 mucus glands at these points (see Fig. 5). The anterior end of each 

 ■ciliated groove can now be easily seen to form a pit-like depression around 

 which the cilia are lashing vigorously. As particles are caught by the 

 •cilia they are seen to be passed along in the middle of the groove towards 

 the mouth, as has been described above.* 



EECAPITULATION OF THE ACCOUNT OF THE FOOD 

 AND EESPIRATOEY CUERENTS IN AMPHIOXUS. 



The main food and respiratory current in Amphioxus is produced by the 

 lashing of the lateral rows of cilia on the gill-bars or gill-filaments (see 

 Fig. 4, I.e., Fig. 3, and Fig. 6). These lateral cilia lash across the length 

 ■of the filament from the cavity of the pharynx to that of the atrium. 

 In the adult Amphioxus there are about 180 gill-filaments on each side of 

 the body (Willey, 1. p. 17). Each of these carries two long rows of lateral 

 •cilia, hence in all there are about 720 rows of long cilia acting like oars 

 lashing water through the body of the animal. These are indeed powerful 

 enough to produce the strong current that is to be observed. 



* If a stronger solution of methylene blue is used the whole of the wheel organ as 

 well as the pharjTix stains a deep blue, and a surprising amount of detail can be made 

 •out over the whole of the body. 



