292 



J. H, ORTON. 



of the filaments collect food-particles and lash them towards the base 

 of the filaments into the food groove (see Fig. 5, p. 289). In the same 

 way the frontal cilia on that part of the lophophore adjacent to the 

 food groove entrap food-particles and lash them along the face of the 

 lophophore either on to the base of the filaments or towards the powerful 

 ciha at the edge of the buccal lip (see Fig. 5). These cilia quickly push 

 the particles under the lip into the food groove. The food-particles, on 

 entering the food groove, are then carried along towards the mouth, as 

 has been stated by Shipley, being rapidly transported thence by very 



Fig. 7. — View of transverse section of five ventral and four dorsal gill-filaments of Crania 

 taken near the lophophore, showing the alternation of the filaments in these two 

 series. 



(The outlines of the sections were drawn with the camera lucida, and the 

 remainder filled in slightly diagrammatically (x about 192.) 



The arrows indicate the directions in which the lateral cilia lash, and it will be 

 seen that those of the smaller ventral filaments lash directly on to the frontal, 

 surface of the larger dorsal filaments. 

 I.e. Lateral cilia which lash across the length of the filament, as indicated by 



the arrows, to produce the main current, 

 f.c. Frontal cilia, which lash along the length of the filament and collect and 



transport food particles, 

 ra. Globules of mucus seen in all the sections on various parts of the frontal 



and lateral sides of the filamentar epithelium. 

 g.s. The gill-filament supports. 



strong cilia. In the process of food-collection the secretion and trans- 

 portation of mucus plays an important part, for the mucus when spread 

 out in thin layers forms an efficient method of capturing and retaining 

 captured food-particles, and is also easily transported in this form by 

 cilia. Mucus serving this purpose is secreted by the frontal epithelium 

 on the gill-filaments and especially by that of the dorsal filaments, where 

 the secreting cells occur chiefly in the trough of the filamentar groove 

 (see Fig. 7, above, and also Van Bemmelen, 6, Taf. 8, Fig. 6, in a section 

 of a gill-filament of Rhynchonella psittacea). Blochmann (10) has 

 described aggregations of mucus cells between the bases of the filaments,, 

 that is, in the buccal groove, and also others scattered over the epithelium 



