INTESTINAL RESPIRATION IN ANNELIDS. 803 



touch on these points, but are concerned with the phenomena which lead one to infer a 

 general respiratory activity of the whole wall of the posterior portion of the intestine. 

 Specimens were found in large numbers at Millport, and a considerable number were 

 examined. It may be mentioned that the animals frequently progress with the posterior 

 end of the body jfirst. 



The existence of a ventral ciliated groove in the hinder part of the intestine, posterior 

 to the accessory gut, has been mentioned previously. Ascending ciliary action is, how- 

 ever, by no means confined to this groove ; the whole circumference of the intestine in 

 its posterior part shows the same ciliary action. The anus is often opened widely for 

 a moment, and then closed ; or it may be held widely open for some time — perhaps 

 20 to 30 seconds, — and it is at such times that the ciliary action is specially obvious. 

 Whether it occurs in the middle region of the body or not cannot be seen, owing to the 

 opacity of the intestine under the microscope in this portion of its extent ; at the point 

 where it ceases to be visible it may be indefinite in direction. In the oesophageal groove 

 also {vide ante), ciliary action is well marked, but does not work in any definite direction. 



Antiperistaltic contractions of the intestine are almost always visible. The waves 

 may be seen to extend, in a quiescent animal, from the anus to the anterior end of the 

 hinder section of the intestine, or some distance in front of this. In other cases they 

 are more restricted in extent. They may begin at the anus and extend forwards for 

 only a few segments, and their rhythm may be irregular. Or they may occur only in 

 the anterior segments of the intestine, just behind the thorax. Or they may occur in 

 the same animal, at various portions of the intestine ; or lastly, the contractions some- 

 times manifest themselves as merely ring-like constrictions of a segment of the gut, 

 which do not progress, but, remaining stationary, after a time relax again. 



ClRRATULID^. 



Cirratulus sp. 



In specimens belonging to the genus Cirratulus observed at Millport, ciliary action 

 was seen around the anus, and particles of carmine in the neighbourhood were agitated 

 and apparently attracted ; some of the particles seemed to be taken into the gut. The 

 animals are however too opaque to allow the presence or absence of ciliary action in 

 the intestine to be determined. 



An antiperistalsis of the same character as in Arenicola ecaudata was observed ; 

 and the anus was opened and closed in the same manner as has been described for that 

 species. 



Terebellid^. 



Polycirrus {? caliendrum). 



Ascending ciliary action was seen in this species just within the anus. 



A more interesting phenomenon, however, and it would seem a more eifective means 



