CILIARY MECHANISMS ON THE GILL IN AMPHIOXUS. 



33 



more quickly than the other simple forms, which feed relatively slowly. 

 The process of food-collection at the anterior end of the pharynx in 

 Ascidia menfula is shown in Fi,<f. 8. At the posterior end of the pharynx 

 in this animal the cilia in the dorsal groove lash food-particles forwards 

 to the oesophageal opening. This process can be easily observed by 

 cutting" from the test a window, through which the processes can be 

 followed distinctly. 



Pig. 8. — A view of the anterior end of Ascidia mentula to show the mode of feeding. 

 Drawn from the living animal, as seen through a hand-lens. A part of the pharynx 

 is drawn as though the test were transparent. ( x ca. A.) 



A. 

 B. 



At. 



En. 



D.L. 



P.M. 



G. 



Arrow indicating the direction of the inhalent current. 



Arrow indicating the direction of the exhalent current. 



Arrow in the atrium showing the direction of the main current after passing 

 through the gill slits. 



Endostyle. 



Locus of the dorsal lamina. 



Food-particles collected into a cylindrical mass with mucus being trans- 

 ported across the gill-bars and away from the endostyle towards the 

 dorsal lamina, as indicated by the dotted arrows alongside. 



One of the longitudinal bars of the gill. 



CILIAKY MECHANISMS ON THE GILL OF ASCIDIANS. 



The main current through the branchial cavity of all the Ascidians 

 examined is produced by the lashings of the cilia on the sides of the gill- 

 bars, as has been observed by Herdman for Ascidia jnentula (10, p. 47). 

 Food-collection is effected by the cilia on the pharyngeal surface of the 



NEW SERIES. — VOL. X. NO. 1. NOVEMBER, 1913. C 



