INTESTINAL RESPIRATION IN ANNELIDS. 793 



No antiperistalsis was observed. The dorsal vessel was, however, contracting ; its 

 contractions are thus quite independent of those of the gut (if these latter 

 ever occur). 



In another species of the genus, of which several specimens were examined, the 

 conditions varied. In two specimens ascending ciliary action was absent ; in a third 

 there was no ciliary movement near the anus, which was closed, but some distance up 

 the alimentary canal an obscure ascending ciliary action was visible. There was no 

 antiperistalsis in any of the specimens ; in one the dorsal vessel was seen to be con- 

 tracting regularly ; so that here also the vascular contractions are quite independent 

 of any contractions of the intestine. 



In another species, probably belonging to this genus, the ascending ciliary movement 

 was observed at the hinder end of the last animal of a chain. No antiperistaltic waves 

 were seen ; contractions of the dorsal vessel were however going on rapidly and at 

 regular short intervals (once every four seconds). Another specimen of the same 

 species showed neither ciliary movement nor antiperistalsis ; it is therefore not to 

 be concluded that reversed ciliary action does not occur in a species because it does 

 not happen to be observed in a particular specimen. 



Other Syllids. 



k. number of other Syllids were examined, but not specifically identified. As repre- 

 sentative of these observations the following may be recorded. 



In a Syllid with well-developed ventricular cseca and well-marked sucking action of 

 the pharynx, ascending ciliary action in the intestine was not visible at first, but could 

 be distinguished later ; it could be made out in nearly all the hinder transparent 

 segments of the intestine, though the anus was kept closed during the whole observation. 

 Antiperistaltic contractions of the gut were also taking place, — at first in the hindmost 

 fourteen segments, but later much further forwards also ; these contractions were quite 

 irregular in rhythm ; each wave extended usually over only a few segments, though 

 sometimes over a larger number, — as many as eight ; sometimes a contractile wave 

 would begin at the posterior end of the animal, sometimes a few segments in front 

 of this, sometimes further forwards. These contractions of the gut were sufficient to 

 constrict the lumen very considerably ; and they and the contractions of the dorsal 

 vessel were quite independent. 



In other species also some degree of ascending ciliary motion was observed in the 

 last segment, or last two segments, of the intestine. 



The above are all cases in which ascending ciliary motion, with or without ascending 

 peristaltic contractions, was observed in the intestine. In many Syllids, however, these 

 phenomena do not occur, or at least did not occur during the time the specimens were 

 under examination. This was the case in Syllis gracilis, as well as in a number of 

 animals which were not specifically identified. 



