HEART-BODY, ETC., OF CERTAIN POLYCH^TA. 291 



With regard to the relation of the heart-body to the coeloraic 

 fluid, the position of the dissepiment sacs must be noted. 

 These are diverticula of the dissepiment, or great anterior 

 septum, which extends transversely across the body-cavity 

 behind the nephrostomes of the most posterior pair of the 

 great anterior nephridia. The heart-body runs in the heart 

 to a point a little beyond where the latter pierces the dissepi- 

 ment. The sacs consequently occupy a position on each side 

 of the heart — a fact which is especially noteworthy in consider- 

 ing the connection of the heart-body with leucocytes, since the 

 dissepiment sacs are generally crowded with corpuscles.^ 



Some of the species of Polycirrus are remarkable among the 

 Terebellidae in lacking blood-vessels, and consequently also 

 gills and heart-body. It is, therefore, not without interest to 

 observe an accumulation of coelomic corpuscles upon a mem- 

 brane supporting the gut in the anterior dorsal region. An 

 area for the origin of the coloured corpuscles may survive at 

 this point. 



These coloured corpuscles, as is well known, occur mingled 

 with the ordinary coelomic corpuscles, the resulting coelomic 

 fluid being termed hsemolymph (Eisig and Meyer). Meyer 

 states (24, B. p. 645, note i), " Abgesehen vou den eigentlichen 

 Lymphkorperchen, noch andere auch freie Zellen in grosser 

 Menge in der Leibesfliissigkeit umherschwimmen, welche 

 durch uud durch von einer Art Blutpigment diirchtraukt 

 siud und somit die RoUe von gefarbten Blutkorperchen zu 

 iibernehmen scheinen." The ordinary corpuscles of which he 

 speaks are amoeboid, and contain considerable masses of amber- 

 coloured pigment insoluble in ether (fig. 29). The ^^blood- 

 corpuscles " are elongated and oval, or sometimes very small 

 and round, and are pale yellow in colour, whilst in vacuoles 

 placed, in the case of the elongated form, at the extremities of 

 the cell, there are often small droplets of a madder-pink colour 

 (figs. 30, 31, 57, 58). Cuenot (9", p. 414) speaks of these 



' It is remarkable in young Polymnia that whilst numbers of eleocytes occur 

 behind tlie dissepiment, they are almost entirely absent from the part of the 

 ccelom anterior to it. 



