HEART-BODY, ETC., OP CERTAIN POLYCHiETA. 271 



the Cirratulidae the dorsal vessel, which often reaches a rlia- 

 meter as great as that of the gut, is almost blocked by it. 



The Heart-body of the Cirratulidae. 



The blood-system of a Cirratiilid has been well figured 

 by Ed. Meyer (24, B), and his observations are confirmed by an 

 examination of young living individuals, and specimens dis- 

 sected and afterwards fixed and cleared. In Audouinia 

 filigera, as in all the group, the dorsal vessel is not confined 

 to the anterior end of the body, but runs back into the 

 abdominal region. At about the fifth segment it gives off a 

 pair of lateral recurrent vessels, which supply branchial vessels 

 in each gill-bearing segment (fig. 1). In an adult stained 

 specimen several vessels are also seen going off directly to the 

 gills, whilst the dorsal vessel itself continues anteriorly as a 

 much-diminished trunk. The heart-body extends forwards to 

 the point of origin of the lateral vessels. There it usually 

 ends in irregular projections which appear on the point of 

 becoming detached ; but it may continue as a broken cord ex- 

 tending for the space of a segment into the fine anterior 

 dorsal vessel. The three brown cords, of which it is typically 

 composed, are constricted at the intersegmental septa, and 

 branched, united, and folded irregularly (fig. 2). Sections 

 reveal the fact that they are connected with the heart- wall at 

 many points by means of fine processes. The greatest develop- 

 ment of the heart-body is at about one third of its length 

 from its anterior end. In the small transparent Cirratulus 

 chrysoderma it may be seen with the low power that at this 

 point, on systole, it almost entirely blocks the lumen of the 

 vessel, the action of which as a blood-propelling organ must be 

 greatly modified. The suggestion by Schaeppi in the case of 

 Ophelia, and by Steen in that of Terebellides Stroemii, 

 that it has a valvular function has been mentioned above. 

 Beddard, in his monograph on Oligochseta, refers to Michaelsen 

 also as saying that it " serves to ease the contractions of the 

 dorsal vessel.^' Michaelsen's view seems rightly applicable to 



