THE PHYLUM CHORDATA 



37 



nc 



nute organic particles, such as protozoa and pelagic larvae. The 

 mechanism for concentrating this dilute food is somewhat complex. 

 The pharynx is lined with ciliated epithelium and the cilia beat 

 inward so as to 

 cause a current of 

 water to be drawn 

 into the mouth and 

 out through the 

 gill-slits. The cilia 

 beat also down- 

 ward, so as to force 

 the current to the 

 floor of the phar- 

 ynx, where there is 

 a hypopharyngeal 

 groove or endostyle J 

 (Fig. 10) fiflecf with 

 sticky mucus to 

 which food parti- 

 cles adhere. The 

 endostyle is pro- 

 vided with strong 

 cilia which whip 

 the mucus into a 

 rope-like mass and 

 drive it forward en- 

 with its burden of 

 food particles to 

 ~ihe anterior end 

 of the pharnyx. 

 There the endo- 

 style bifurcates 

 around the mouth 



mf 



FIG. 10. Transverse section through the pharyngeal 

 region of Amphioxus. a, atrial cavity; c, ccelomic cav- 

 ity; df, dorsal fin fold; en, endostyle; fr, *fin ray; I, liver 

 diver ticulum; m, myotome; me, myocomma; mf, meta- 

 pleural fold; n, notochord; nc, nerve cord or spinal 

 chord; ne, nephridium; p, pharynx; pc, pharyngeal cleft; 

 sg, supra-pharyngeal or dorsal groove. (Redrawn and 

 modified after Lankester and Boveri.) 



in the form of 



two semicircular 



grooves, the peri- 



pharyngeal bands, which unite again above the mouth and form 



the dorsal or hyperpharngeal groove (Fig. 10) . The mucous rope travels 



backward in the dorsal groove till it reaches the stomach and intes- 



