FEEDING REACTIONS IN DILEPTUS GIGAS. 1 17 



tures are capable of enormous expansion at the time of feeding. 

 Normally, however, they are closed except for a pit-like cavity 

 which is always present. A cytopyge is sometimes discernible near 



FIG. i. Diagrammatic sketches of Dileptus gigas: A. side view; B, oral 

 view ; v, contractile vacuoles : p, proboscis ; m, mouth ; c. cross section of pro- 

 boscis ; r, bands of large cilia. 



the posterior end, at which place faecal material often collects in a 

 large vacuole from which it is sporadically discharged. There are 

 numerous contractile vacuoles of which the larger ones are ar- 

 ranged in a series near the aboral surface. Thin contractile 

 fibrillae extend around the body in the form of a flat spiral, effect- 

 ing about one complete turn for the entire length of the body. 

 The entire body is covered with short cilia which run in rows 

 parallel to the fibrillce. On the ventral surface of the proboscis, 

 which is somewhat flattened, the cilia are considerably thicker and 

 longer than elsewhere, especially along the edges, where they are 

 in the form of two bands. These extend backward in such a way 

 as to meet and form an arch just behind the mouth opening. 

 Since all these cilia beat backward under normal conditions, a 

 decided current is produced in the groove between these two bands 

 of large cilia. This current starts at the tip of the proboscis and 

 runs back to the mouth, where it ends in a sort of vortex, due to 

 the action of the band of cilia which partially surrounds this pit- 

 like orifice as above described. Structures which have been quite 

 generally described as trichocysts are found in the oral surface of 

 the proboscis. They can be seen only indistinctly in living mate- 



