HEART-BODY, ETC., OP CERTAIN POLYOH^TA. 283 



body, the peritoneum, the detached cell-heaps, the amoeboid 

 corpuscles, and finally the great anterior nephridia — trace out a 

 path by which they may be removed from the blood to the 

 body-cavity, and thence to the exterior. 



Characteristics of the Heart-body in other Poly- 

 chseta. — The organ in the Chlorhsemidse, Terebellidse, and 

 Amphictenidse has much in common with that in the Cirra- 

 tulidse, but each group shows peculiarities. Of the two other 

 groups which are included in Dr. Benham's classification, 

 under the head of Terebelliformia, Sternaspis has no heart- 

 body proper, and the Ampharetidse are rare at Naples. 



Chlorhaemidse. — The dorsal vessel is, unlike that of the 

 Cirratulidse, confined to the anterior end of the worm. It 

 arises at the opposite side of the digestive tube to the point of 

 attachment of the stomach, and the blood from the sinus 

 which surrounds the digestive organs flows into it. It is a 

 broad trunk, lying dorsal to the oesophagus, and after its point 

 of origin quite separate from the alimentary canal. It narrows 

 towards its anterior end, and eventually divides into two 

 branchial vessels. In Siphonostoma, Cunningham (10) aptly 

 describes the heart-body which occupies this vessel as a folded 

 band, which in section branches dorsally ; he also states that it 

 contains no lumen, though the cells of the opposite sides are 

 in a definite line of contact. Jourdan (17), writing the same 

 year, 1887, stated, on the contrary, that there is a lumen, and 

 gave a figure showing it. 



Now, on examining a series of transverse sections, it is 

 clearly seen that the " band^' is formed of a cylindrical tube, 

 the walls of which have been compressed together, and that 

 though the single cell-layers which form the walls ^ are in 



the cells that contain them, that is the side towards the gut, and are probably 

 of a dififerent nature from that of those discussed. 



' If an endothelium covering the heart-body exist, it must be extremely 

 attenuated. One or two nuclei on the surface of the organ seem to suggest 

 its presence. Bles states that the gut wall is directly bathed in blood, but 

 there, too, it is not impossible that an extremely attenuated membrane is 

 interposed. All the structures of Siphouostoma are so thin, the solid jelly 



