ON CILIARY MECHANISMS. 305 



have the same function as the similar groups of glandular cells in a similar 

 position in Amphioxus and Ascidians. The cilia on the endostyle of 

 Crepidula and Calyptrgea lash mucus and food-particles on to the gill as 

 has already been stated, but there is also a ciliated groove on the left 

 side of the endostyle which lashes some mucus and captured food-particles 

 forwards (see Fig. 10). This forward stream of mucus contributes largely 

 to the forward stream in the mantle cavity which has already been de- 

 scribed (1, p. 448), and whose function is chiefly that of entrapping the 

 coarser food-particles at the entrance to the inhalent chamber. By means 

 of the mucus which is thus carried along this ciliated channel a large 

 proportion of the larger and often innutritions particles become lodged 

 in the food-pouch in the middle of the front portion of the mantle, and are 

 either rejected or eaten by the animal, as has already been observed 

 (1, p. 448). In this way and to this extent these animals are able to select 

 their food. 



The character of the endostyle of Crepidula may be gathered from the 

 views shown in Figs. 10 and 11, and the transverse section shown in Fig. 12. 

 From the transverse section it is seen that there are two rows of long 

 glandular cells with basal nuclei, and between and to the left of 

 these rows is a line of curious ciliated cells with an apical or distal 

 nucleus. On either side of the endostyle, the epithelium consists 

 of columnar ciliated cells, which become more cubical as they 

 recede from the endostyle. The epithelium on the right side 

 (seen on the left in the section) passes into that of the floor of the 

 mantle cavity. In the latter region the cilia lash away from the 

 endostyle towards the right side of the mantle cavity, and while thus 

 assisting in producing the main current, at the same time help in collect- 

 ing food-particles into the food-groove on the right side of the floor of 

 the mantle cavity (see Fig. 10, p. 302). The characters of the endostyle 

 and the ciliation of the mantle are the same in Calyptrsea as in Crepidula. 

 In Capulus these characters are also the same in the living animal, but 

 sections of the endostyle have not yet been examined. 



The remarkable likeness of the endostyle of Crepidula and its allies to 

 that of Amphioxus and Ascidians becomes still more evident when it is 

 compared — as it should be — to a half, the right half, of that of Am- 

 phioxus and Ascidians : for it is to be remembered that there is only 

 one half of a ctenidium and only one series of filaments present in Crepi- 

 dula, whereas both a right and left series of " filaments " exist in Am- 

 phioxus and Ascidians. When, therefore, the endostyle of Crepidula is 

 compared with the right half of that of Amphioxus and Ascidians it will 



