98 University of California Publications in Zoology [VOL. 13 



posterior peripheral current, beginning immediately posterior to the 

 level at which the oesophagus passes through the boundary layer, is 

 obliquely posterior and to the right, i.e., following the general direction 

 of the oesophagus. At the posterior limit of the sack the direction 

 of the current changes so as to flow towards the left dorsal wall. (2) 

 The anterior current beginning at this point follows the left wall of 

 the sack, passing obliquely anteriorly and somewhat ventrally, i.e., 

 in exactly the opposite direction to the posterior current. When the 

 current reaches the anterior extremity of the entoplasmic sack, which 

 extremity, as will be remembered, is anterior to the opening of the 

 oesophagus into the sack, it is again directed posteriorly. (3) The 

 internal posterior current flowing internally to the first described 

 posterior current passes posteriorly to the region of the caecum, where 

 it becomes lost in the anterior current. Thus we see that the two 

 posterior currents, i.e., peripheral and internal, pass in the same 

 direction as does the oesophagus, and so may assist in drawing food 

 particles into the entoplasm ; also that by reason of its flowing directly 

 toward the caecum the internal current may assist in carrying waste 

 products to the organ of defecation. 



Most interesting of all the observations, however, were those upon 

 the action of the dorsal and adoral membranelle zones together with 

 that of the operculum. First of all, it was noted that in swimming 

 the organism uses both zones of membranelles and that normally the 

 contractions take place as waves passing from one extremity to the 

 other. In the case of the dorsal row of membranelles these waves 

 usually started at the left extremity in the following manner : The 

 first membranelle is made to circumscribe a conical space, the base 

 of which corresponds to the distal extremity of the membranelle and 

 the apex of which corresponds to its attachment to the bo(|y, i.e., 

 circumduction. The direction of this movement is clockwise and the 

 movement has no sooner started in the first membranelle than it is 

 begun in the second, and so on. Even when the animal is swimming 

 slowly a second wave may be started before the first wave has reached 

 the opposite extremity. Thus two or three waves of contraction may 

 be passing along the row of membranelles at the same time. In the 

 case of the adoral membranelles the movements are made out with 

 much more difficulty and it is only when the adoral region faces the 

 observer that satisfactory results can be obtained. It is sometimes 

 possible to bring the animal into this position by a careful manipu- 

 lation of the cover glass. In general the movements of the adoral 



