CILIARY MECHANISMS ON THE GILL IN AMPHIOXUS. 31 



wiiich in turn carries the food-mass upwards into the dorsal groove, and 

 at the same time assists in capturing food-particles. Delage and Herouard 

 (3, p. 144) point out the differences in the descriptions of this process, and 

 cautiously give only a general account. 



FOOD-COLLECTION IN" VARIOUS ASCIDIANS. 



Observations have been made on a number of Ascidians, namely^ 

 Ascidiella aspersa, Phallusia mamillata, Ascidia mentula and virginea, 

 Ciona intestinalis, Clavellina lepadifonnis, Leptoclinum {Diplosoma} 

 yelatinosum and a species of MorcJiellium, with the result that the 

 process of food-collection has been found to be the same in all these 

 animals as that described by Fol and Roule. 



When carmine particles are added to the water in which one of these 

 animals is living, for example, Ascidia mentula, the particles may be 

 observed with a hand lens to be drawn into the branchial cavity and 

 against the wall of the gill. Particles approaching the endostyle, however, 

 are seen to be immediately lashed out of this groove on to the wall of the 

 pharynx, just as is the case in Amphioxus. These particles become rolled 

 into a mass with mucus, and are transported across the branchial sac to 

 the dorsal lamina. All the particles entering the endostyle are washed 

 out on to the pharynx in this way, and no mass of collected food has 

 ever been seen — in any of the animals examined — to be passed forwards 

 along the endostyle. An examination of the endostyle through a micro- 

 scope shows further that the lateral rows of cilia on this organ lash in a 

 direction across the endostyle, and from the endostyle on to the pharynx, 

 and no transference of food-particles along the endostyle is seen. The 

 food-particles drawn against the pharynx become caught in mucus and 

 gradually transferred across the wall of the pharynx to the dorsal lamina,^ 

 becoming rolled into cylindrical masses with mucus on the way. This 

 process of food-collection and transportation is very well seen in the 

 Compound Ascidian Leptoclinum {Diplosoma) gelatinosmn, as shown in 

 Fig. 7, which is a drawing of one living zooid in the act of feeding. In 

 such a small animal as this one is able to keep the whole animal in the 

 field of a microscope, and so to follow the course of even small food- 

 particles in the pharynx. The particles entering the branchial cavity 

 sometimes fall on to the pharyngeal wall close to the peri-pharyngeal 

 grooves, but in none of the animals examined have the particles posterior 

 to the grooves been observed to be drawn into these grooves. On the 

 contrary, in Ascidiella aspersa especially these food-particles become 

 collected in masses some distance posterior to the peri-pharyngeal groove 



