INTESTINAL RESPIRATION IN ANNELIDS. 791 



is strange tliat Malaquin does not mention the ascending ciliary current in the posterior 

 part of the intestine of many of these forms ; and that he does not consider the 

 possibility that the colouring matter of his experiments, which was deposited in the 

 wall of the posterior intestine, might have been directly introduced at the anus. 



Lang (29) mentions that Steen observed antiperistaltic contractions of the intestine 

 in Terebellides stroemii, and Wiren similarly in a number of families of Polychseta. 

 Goodrich (22) is acquainted with the postero-anterior action of the intestinal cilia 

 in Syllids. 



I may add two references to general zoological treatises. Gegenbaur (21) says: 

 " The hindgut of many Annelids may be seen to take in water, and this may be con- 

 nected with a respiratory function of this division of the intestine." Similarly, Benham 

 (4) : " Many Chjetopods take in water by the anus — no doubt for respiratory purposes 

 — and pass it forwards along the intestine." 



2. Observations on Polychseta. 



Though the third of the modes of respiration specified in the foregoing section is 

 much the commonest and most widely distributed in the Polychseta, it is the one which 

 has hitherto, as may be seen from the historical account, received the smallest amount 

 of attention, at least in print. Students of the group are probably, indeed are almost 

 necessarily, familiar with it ; but the details of the process, and its actual distribution, 

 have received no extended treatment. 



The following observations deal for the most part with this mode of respiration, — 

 with respiration through the general internal surface of the intestine, by means of the 

 introduction of water at the anus, but without specially differentiated mechanism. It 

 may, however, be noted here that the mode of alimentary respiration which occurs in 

 Aphrodite aculeata is not strictly to be included under any of the three headings 

 previously enumerated ; in this animal the respiratory water, though expelled from the 

 anus, is not taken in there, but at the mouth, and passes as a regular and voluminous 

 current through the whole of the alimentary tract. I have also included some observa- 

 tions on the phenomena to be seen in the posterior portion of the intestine of Capitella 

 capitata, though I have nothing to add concerning the " Nebendarm." 



The observations here recorded are distributed over the majority of the families of 

 Polychseta. They could, of course, be extended, and it was ray object so to extend them 

 as to include representatives of at least all the more accessible British families ; but an 

 unfortunate attack of illness cut short my time at Plymouth, and so prevented me from 

 carrying out my plan in full. 



Syllids. 

 Trypanosyllis zebra. 

 In a specimen which was undergoing asexual division, ciliary action in an ascending 

 direction, so violent as to be seen with a small dissecting microscope, was observed in 

 TRANS. ROY. SOC. EDIN., VOL. XLIX. PART III. (NO. 14). 108 



