104 A. OKA. 



developed except near the aiiu.-^, where it f(3nns a sort of si)hincter. 

 The anus when expanded is us wide as the widest part of tlie in- 

 testine, but when contracted it closes altogether. The outer cell- 

 Inyer is similar in all respect with that of other parts of the alhnentary 

 canal. At the point where the intestine is tightly pressed against 

 the oesophagus, the outer layer of the former ])asses directly into that 

 of the latter, bringing the cells of the inner layers of both organs in 

 C(3ntact. 



3. Tentacles. 



The tentacles are arranged in one continuous series along the 

 outer and the inner margin of a horse-shoe shaped lophophore, as 

 mentioned before. They are hollow cylindrical organs measuring 

 1 mm. in length, and 0.03 mm. in breadtli. They are t(3 be con- 

 sidered as prolongatioiis drawn out, as it were, from the endocyst. 

 In the living state, they are freely movable in every direction at the 

 will of the animal, but I have never seen them coil or contract. 

 Generally, they stand nearly parallel to one another in graceful 

 curves (fig. 2, PI. XVIL). 



The cross section of a luphophoral arm (tig. 30, PI. XIX.) is 

 almost semicircular in outline, slightly convex above and rounded 

 below, measuring 0.3 mm. in breadth, and nearly as much in depth. 

 The ciliati(3n on the upper surface is distinctly visible on sections. 



The cells of the outer layer of the tentacular wall have all the 

 essential characters of those of the endocyst. They rest on a fine base- 

 ment membrane and are furnished each with a long cilium (fig. 16, 

 PI. XVIII. (Jut. lay.), constantly vibrating in a certain fixed direc- 

 tion. The ciliation ofthat side of the tentacles turned away from the 

 mouth drives the water upward, while that on the opposite side tends 

 to drive it toward the mouth below. The iiiner layer of the tentacles 



