INTESTINAL RESPIRATION IN ANNELIDS. 781 



Both at its first origin, then, and generally at the present day, this is the function 

 of peristalsis. If now we say, with Lang, that its original function in the Annelida 

 (the statement is not, in Lang's Thesis 21, restricted to Polychseta) was ("perhaps") 

 circulatory, we assume a different origin for the contractions ; we renounce the 

 possibility of deriving them from the peristaltic contractions of the alimentary tube 

 of lower forms, which are concerned with ingestion, and must suppose them to have 

 arisen de novo for the purpose of circulating the fiuid contained in the substance of 

 the gut- wall. 



It seems to me preferable to connect the peristaltic action of the intestine in 

 Annelida with similar phenomena in lower forms ; to suppose that it existed before the 

 circulatory system was evolved ; and to hold, therefore, that its primary object was 

 the movement of matters within the lumen, and that its circulatory function is secondary. 



Vejdovsky (55, 56), basing his conclusions on refined histological researches, has 

 recently put forward views on the origin of the vascular system in the Annelida which 

 conflict in certain points with the theory of Lang. 



Choosing the Enchytraeidse as a starting-point, Vejdovsky shows that the perienteric 

 sinus is crossed by thin protoplasmic strands passing between certain basal replacing 

 cells of the intestinal epithelium, which bounds the sinus on its inner side, and a 

 connective-tissue-like membrane which limits it externally ; intimately associated with 

 this membrane are a number of flattened, hemispherical, or sometimes stalked cells, 

 which project into the sinus. External to the membrane are the muscular coats of the 

 intestine and the chloragogen layer. The membrane (vasothel) is interpreted as having 

 been separated from the intestinal epithelium, the cells in connection with the vasothel 

 as having migrated outwards from the layer of replacing cells, and the strands which 

 cross the cavity of the sinus as constituting evidence of the original unity of the outer 

 with the inner wall of the sinus. The sinus is therefore contained within the entoderm. 



The dorsal vessel possesses two muscular layers, a circular and a longitudinal, 

 continuous with the muscular coats of the intestine. Within these there exists the 

 same vasothel, with the same hemispherical or stalked cells, as was found in the wall 

 of the intestinal sinus ; the cells possess processes in which fine fibrils, staining black 

 with iron-hsematoxylin, are demonstrable ; they have, therefore, the character of muscle- 

 cells. The other vessels have a fundamentally similar constitution ; the cells of the 

 vasothel, however, may assume different forms, such as, for example, an elongated pear- 

 shape in those cases where they are aggregated to form valves, a cubical shape where 

 they form the rod-like cardiac body. 



In the higher families (Tubificidse, Megascolecidse, Lumbricidse, as represented by 

 RhyncJielmis, Phei^etima, and Dendrohgena) the constitution of the vascular system 

 is essentially the same as in the Enchytrseidse. 



Vejdovsky sums up the theoretical conclusions to be drawn from his observations as 

 follows : — " Sie zeigen vor allem, dass der sog. Darmblutsinus die urspriinglichste 

 Komponente des Gefasssysteras vorstellt und dass dieser Sinus ein integrierender 



