350 



11. oiisiiimA : 



anterior. Posteriorly it opens into the hind-gut with a narrow con- 

 striction at the end of the ventral side. The hind-gut bulges out 

 anteriorly to form a cecum, the flattened dorsal surface of which is 

 in close contact with the mid-gut. The shape of the hind-gut, 

 including the caecum, is oval in ventral aspect, but somewhat 

 triangular in side view. It is of a colour similar to, but slightly 

 lighter than, that of the mid-gut. The anus opens on a low prom- 

 inence of the anal field. 



Chun's statement that the ciliary bands along the oral field 

 seem to execute a food-wafting motion, could be experimentally 

 verified by adding some powdered carmine into the water containing 

 the living larva. At the time when the mouth is opened, there 

 arises a flow of water in the oral groove, which carries the powder 

 gradually towards the mouth. The powder is allowed to enter the 

 mouth, and is then driven into the mid-gut by quick swallowing 

 action, which occurs immediately after the mouth is closed. At this 

 moment the above mentioned constricted end of the oesophagus sinks 

 slightly into the latter. The powder travels slowly through the 

 mid-gut towards its posterior end, to pass into the hind-gut. In this 

 last section of the alimentary canal, it is caught by the revolving 

 current of the watery contents caused by the action of the cilia of 

 the wall. Thus the powder continues for some time to circle round 

 in the hind-gut, until it is finally emitted through the anus. I have 

 never observed periodic contraction of the hind-gut ; nor did there 

 yet exist bud-like rudiments of the tree even in the largest specimen 

 observed. 



The posterior enterocoels of both sides (fig. 3, Ipe and rpe) run 

 along the whole length of the mid-gut, and are in the large speci- 

 mens dorso-ventrally somewhat extended so as to embrace the latter 

 to a degree. 



It is highly interesting to notice that in the large specimens 

 there is already formed the primitive ring canal or the hydrocod 



