INTESTINAL RESPIRATION IN ANNELIDS. 779 



became more and more subservient to the needs of the circulation ("Die Kontraotionen 

 der Gonocolwande . . . konnten sich immer mehr und immer spezieller in den Dienst 

 dieser Blutbewegung stcllen "). 



As will be apparent from the foregoing, the contractility of the blood-vessels is to 

 be derived from the antiperistaltic contractions of the gut (which had not at first a 

 specially circulatory significance) ; and these are to be looked on as a primitive charac- 

 teristic of the alimentary canal [vide post, p. 780). 



(3) Thesis 20 runs as follows: — " Dass die Darmmuscularis urspriinglich dem 

 Darmepithelrohr fremd ist, erhalt eine interessante Illustration durch die vielfach 

 beobachtete Tatsache, dass ihre Kontraktionswelle bei den mit einem Darmblutsinus 

 ausgestatteten Polychaten antiperistaltisch verlauft. Sie dient hier nur als propul- 

 satorischer Apparat des vom Darmsinus in das Riickengefass stromenden Blutes." The 

 limitation (bei den mit einem Darmblutsinus ausgestatteten Polychaten) is needless ; 

 the contractions are antiperistaltic in the aquatic Oligochseta, and also, as will be shown 

 in the second part of the present paper, in a number of families of Polychseta which 

 do not possess a perienteric sinus. 



Lang apparently here bases himself on Wiren's statements with regard to the 

 Polychaeta (p. 206): " Die fast immer stattfindenden peristaltischen Bewegungen der 

 Ringmuskulatur schreiten bekanntlich von hinten nach vorn fort. Sie haben also eine 

 andere Aufgabe als die Nahrstoffe zu bewegen " ; but this purpose is not respiratory, 

 for " der hauptsachliche und wahrscheinlich der einzige Zweck der peristaltischen 

 Bewegungen ist, wenigstens bei denjenigen Anneliden, welche in der Darmwandung 

 eine grosse, mit Blut ausgefiillte Lakune besitzen — und dies scheint wenigstens bei 

 alien sedentaren der Fall zu sein — das Blut der Darmwandung vorwarts zu treiben." 



The statement which I here wish to oppose, which occurs in the quotations from 

 both FjANG and Wiren, is that the antiperistaltic contractions of the intestine in the 

 Polychaeta are altogether circulatory in their purpose, and not at all respiratory. In 

 the first place, the antiperistaltic movements are associated apparently for a common 

 purpose, and in Polychaeta as well as in Oligochaeta (as a reference to the second part 

 of this paper will show), with an ascending ciliary action, which can have no effect on 

 the circulation. Secondly, the antiperistaltic contractions are usually much more 

 violent than would be necessary for the movement of the fluid in the intestinal network, 

 since they cause a considerable constriction of the alimentary tube and may even 

 entirely occlude its lumen ; they have therefore presumably some other function than 

 the circulation to subserve, and this can hardly be other than the forward propulsion 

 of matters in the alimentary canal, i.e. largely of fluid introduced at the anus, where 

 the antiperistaltic contractions begin and are usually most violent. Thirdly, the 

 combined effect of antiperistalsis and ascending ciliary action demonstrably is to 

 introduce fluid into, and to propel it along, the alimentary canal {cf. also the observa- 

 tions on Polychseta in Part II., and especially pp. 804, 811, on the "gulping" 

 action of the anus and the antiperistaltic waves which follow on this) ; the result must 



