1914] Sharp : Diplodinium ecaudatum 77 



Oral cilia. — The oral cilia {or. cil., figs. A, B, C ; pi. 3, fig. 2; pi. 4, 

 fig. 3) are not only exceedingly fine but are also exceedingly thick, 

 thus making it difficult to arrive at any very definite conclusion regard- 

 ing their size, number or arrangement. It is certain, however, that 

 they are in some way connected with the same motor apparatus as is 

 the adoral row of membranelles, of which they seem to be the direct 

 continuation. In life they appear as minute tufts which are in almost 

 constant motion. They completely surround the oral opening and 

 extend down into the oesophagus for a short distance. They appear 

 to have only one set of roots, which lie close to the oesophageal wall 

 and end in or near the circumoesophageal ring (cir. oes. ring, figs. B, 

 C ; pi. 4, fig. 3 ; pi. 6, fig. 15 ; pi. 7, fig. 33 ) . 



Organs op Food-taking 



The organs of food-taking, ectoplasmic in nature, embrace a cyt- 

 ostome, mouth, or oral opening {or., figs. A, B, C; pi. 7, figs. 20, 21), 

 oral cilia {or. cil.), oral disk {or. disk), to some extent the adoral mem- 

 branelles {ador. m.), and an oesophagus {oes.). 



Cytostome. — The cytostome, mouth or oral opening {or., figs. A, 

 B; pi. 4, fig. 3), is an elliptical aperture almost entirely surrounded 

 by the oral cilia and located at the very anterior extremity of the body, 

 close to the ventral side and inclined somewhat ventrally and to the 

 left. The structure of the oral cilia and adoral membranelles has 

 been described above; their function we shall refer to later. The 

 mouth opens directly into an oesophagus. 



Oesopliagus. — The oesophagus {oes., fig. B; pi. 4, figs. 3-5; pi. 

 7, figs. 20-33) extends, as a closed tube, from the mouth opening to a 

 point slightly below the level of the anterior extremity of the macro- 

 nucleus (pi. 7, fig. 27). At this level the inner wall disappears and 

 the oesophagus descends as an open or one-sided tube to the extreme 

 posterior limit of the entoplasm (pi. 7, figs. 31, 32). At the oral end 

 it is exceedingly small and rather irregularly elliptical in cross-section, 

 with the long axis of the ellipse extending transversely from right to 

 left. It gradually grows larger as it descends posteriorly through the 

 ectoplasm into the entoplasm, and swings obliquely to the right in 

 such a manner that its ventral or outer wall, which is much the thicker 

 of the two walls, approaches and finally comes to lie next to the right 

 side of the body {oes., pi. 4, figs. 4, 5; pi. 7, figs. 23-30). Soon after 

 entering the entoplasm the dorsal or inner wall, which, owing to the 

 oblique descent of the oesophagus, is now turned toward the left, dis- 



