1914] Sharp: Diplodinium ecaudatum 69 



structures with the exception of a single, or possibly a double, layer 

 of alveoli adjacent to the boundary layer, but appears to be a more 

 or less homogeneous mass containing food particles surrounded by 

 food vacuoles. The entoplasm is entirely surrounded by the sack-like 

 boundary layer, is kept from flowing out through the mouth, under 

 normal conditions by the constriction of the oesophageal walls, and 

 from flowing out through the anus by the boundary layer covering 

 the rectum and caecum. Scattered throughout the entoplasm are food 

 particles surrounded always by a food vacuole {fd. vac, pi. 4, figs. 

 3-5 ; pi. 6, figs. 14-19 ; pi. 7, figs. 25-33) . 



Eberlein (1895, p. 244) describes, in the case of Ophryoscolex 

 inermis, ''A¥aben" of the entoplasm, which group themselves around 

 and enclose in a regular manner the bits of food which the animal has 

 taken in. No such structure is present in D. ecaudatum, but it must 

 be noted that, while in the case of 0. inermis the food consists almost 

 wholly of cellulose fragments, in the case of D. ecaudatum and all of 

 its forms the food consists almost entirely of bacteria. Evidence of a 

 vegetable food ingestion in D. ecaudatum appears only in those cases 

 in which the host (ox) has been fed just before slaughtering. After 

 the ox has fed on alfalfa hay the entoplasm of D. ecaudatum contains, 

 for two or three hours only, green chloroplastids, as well as the bac- 

 teria, but no cellulose fragments. In living animals, during feeding 

 periods, a definite streaming of the entoplasm is discernible. This 

 streaming of the entoplasm will be described under observations on 

 the living animals. 



Organs of the Body 



Macronucleus.- — The macronucleus {mac, pi. 3, figs. 1, 2; pi. 4, 

 figs. 3, 5; pi. 7, figs. 29, 33), is situated in the ectoplasm between the 

 boundary layer and the cuticle on the right dorsal side of the body. 

 In general the macronucleus has a rather constant size, shape, and 

 position within the animal. Its anterior end is the larger, is some- 

 what curved, and the longitudinal axis is slightly twisted from left 

 to right. The size of the macronucleus is deserving of special mention. 

 Its longitudinal dimension is equal to about five-eighths of the entire 

 length of the body, and its transverse diameter throughout the greater 

 part of its length is about one-fourth that of the cross-section of the 

 body. Its anterior end is large, bluntly rounded off and situated just 

 internal to and just below the base of the right extremity of the dorsal 

 membranelle zone. It curves slightly dorsad and towards the posterior 



