7U 



PROFESSOR J. STEPHENSON ON 



direction, and does not seem easy to account for. It may, however, be suggested that 

 the postero-anterior stream of water along the intestinal wall, occasioned by the ciliary 

 movement, must have as its complement an antero-posterior axial stream of water 

 returning to tlie exterior at the anus, since it is not to be supposed that the postero- 

 anterior current passes through the whole length of the animal and out at the mouth ; 

 and it is possible that the rotation about an axis of the matter in the intestinal canal 

 may be in some way due to the combined action of these two (;urrents. Harmer (23) 

 describes a rotatory movement of the faeces in the I'olyzoa as being due to the intes- 

 tinal cilia. 



The fteces may pass out at the anus without the ascending ciliary action being 

 suspended — a demonstration of the axial antero-posterior stream assumed above. 



Stommary. 



The following list includes all the JMicrodrili which I have hitherto examined with 

 reference to these phenomena ; the occurrence of antiperistalsis and ascending ciliary 

 action, or their absence, is noted against each : — 



Except in a single specimen of Fridericia bulbosa. 



