804 PROFESSOR J. STEPHENSON ON 



of propelling water along the intestine, is the antiperistaltic action of the intestinal walls. 

 The contractile waves begin at the anus, and proceed upwards for a considerable distance 

 — about one-third of the length of the body. They are regular and strong ; their 

 amplitude may be illustrated by saying that in diastole the intestine almost fills the 

 body-cavity, while in the contracted condition it is reduced to a mere cord, the lumen 

 being occluded. In the middle third of the body also there are to be seen frequent 

 antiperistaltic waves which occlude the lumen of the canal ; they are not however 

 continuations of the posterior series, which do not get as far forwards as this. 



The anus is opened fairly widely at intervals corresponding to those of the intestinal 

 contractions, and is regularly closed at the beginning of each antiperistaltic wave. 

 Thus there is a sort of gulping action ; the antiperistaltic contractions appear to pass 

 forwards the water which has been taken in at the open anus. 



This action was illustrated by the behavioui- of a mass of fsecal matter, which while 

 being expelled was partly drawn in again. Carmine particles introduced near the anus 

 are rapidly aggregated into flocculi by mucus ; these flocculi were also sucked in at the 

 anus ; some were actively expelled shortly afterwards. A large mass of carmine was also 

 drawn in, and after ascending the intestine for a few segments was rapidly shot out 

 again. Another mass sailed in and immediately ascended about six segments up the 

 intestine. Minute particles were wafted in in numbers. 



The carmine experiments do not prove that the matter — the solid matter, at any 

 rate, — which is taken in at the anus ascends the intestine for any great distance ; the 

 particles did not by any means reach the anterior limit of the antiperistaltic waves. 

 From the forcible way in which the larger particles were expelled, it seemed as if there 

 was an active rejection of such masses ; and it is possible that water containing only 

 substances in solution, or, at most, minute particles of solid matter, is propelled upwards 

 to a considerable distance. Such at least is the impression given by the gulping action 

 of the anus and the very strong and regular antiperistalsis of the intestine. 



Genus Amphitrite. 



In a species belonging to this genus examined at Millport there was no evidence of 

 reversed ciliary action in the intestine ; antiperistaltic contractions occur, similar to 

 those described above in Polycirrus. 



In a young semi-transparent specimen, performing slow writhing movements in a 

 dish, the anus was seen to be periodically opened and somewhat everted, appearing 

 almost trumpet-shaped ; after a short time it was retracted and closed, and at the same 

 instant an antiperistaltic wave started from the anus and passed forwards for some 

 distance. The sequence of events gave the impression that a gulp of water had been 

 taken and was being passed along the intestine. 



Carmine particles in suspension also enter the intestine, and may reach a distance 

 equal to a quarter of the length of the body from the anus. 



