SOME POINTS IN THE ANATOMY OF POLYCH^TA. 265 



visible in the centre of this cord, and the cells are so arranged 

 as to form radii passing from the wall of the cord towards the 

 centre. 



Fam. CirratulidjE. 



In Cirratulus cirratus there are three longitudinal 

 cylindrical cords occupying nearly the whole cavity of the 

 dorsal vessel. Two of the cords occasionally anastomose and 

 then separate again. The cells filling the cords are elongated, 

 pale, and nucleated ; the nuclei stain but the rest of the cells 

 remains uncoloured in staiued preparations. There is no 

 lumen, and the cells are not arranged in regular radii, but are 

 placed so that the longer axis passes from the dorsal side of the 

 cord to the ventral. The cells contain large numbers of the 

 usual granules, which are brown and spherical, and usually 

 more numerous near the exterior of the cord than in the 

 central part. In one specimen I found only two cords present 

 of which the dorsal was the larger. The cords are quite free 

 in the interior of the vessel, and have no connection with the 

 walls of the latter (fig. 21). 



The cardiac body is present in the families Chlorhajmidse, Cir- 

 ratulidse, Amphictenidse, Ampharetidse, and Terebellidae. The 

 three last are closely allied, but neither of them has auy other 

 points of close agreement with either of the two first mentioned ; 

 nor are the Chlorhsemidse and Cirratulidse at all connected with 

 one another. The cardiac body is present in every species 

 belonging to the families mentioned, though it varies in details 

 of structure in different species. 



In the heart of Polyophthalmus pictus Edouard Meyer 1 has 

 described an organ which Horst claims as the homologue of the 

 cardiac body we have been considering. It is, of course* 

 probable enough that Horst is right, but it must be remembered 

 that Meyer's description is not complete enough to decide the 

 question whether the organ in the heart of Polyophthalmus is 

 similar in structure to the true cardiac body. Meyer says 

 that a peculiar organ having the form of a thick, short tube, 

 1 ' Arch. f. Mik. Anat.,' Bd. xsi. 



