SOME POINTS IN THE ANATOMY OP POLYCH.ETA. 263 



cannot usually be seen in them ; the most internal, those 

 nearest to the lumen, are almost spherical, and they project 

 separately and at various levels into the lumen, just as do the 

 similar cells in a section of a nephridium. Indeed, the whole 

 structure recalls that of a nephridium very forcibly. Usually 

 the lumen of the tube contains debris which is stained by car- 

 mine, and among this can be recognised spherical cells similar 

 to those which project from the epithelium in process of dis- 

 integration. It is difficult to resist the conclusion that these 

 tubes are glands, but I have been unable to discover any trace 

 of an opening from the cardiac body either to the exterior of 

 the body or into any other organ. In many of the cross 

 sections of the cords no lumen can be seen ; in some cases this 

 is obviously due to the fact that the plane of the section is too 

 near the surface of the cord, and has therefore passed only 

 through the epithelium ; in other cases the plane of the section 

 is median longitudinal, or transverse, through the widest part 

 of a cord, and yet no lumen is seen, the epithelium on one side 

 being so thick as to come into contact with that of the other. 

 It is probable that the obliteration of the lumen is partly due 

 to the contraction produced by reagents. The sections of the 

 cords in any section of the heart of Trophonia are small and 

 numerous, and the whole cardiac body almost fills up the entire 

 cavity of the heart, from its thick posterior portion to its thin 

 anterior region ; the channels left for the passage of the blood 

 are in consequence very small. The blood contains small oval 

 corpuscles, each showing a relatively large, well stained nucleus. 

 These corpuscles are not numerous. 



The cardiac body in Flabelligera affinis (Siphonostoma) 

 presents a great contrast to that of Trophonia in its size re- 

 latively to that of the heart; in the former species the organ 

 constitutes an irregular flat, folded band, running longitudinally 

 through the cavity of the heart and occupying only a small 

 portion of that cavity. Between the cardiac body and the wall 

 of the heart is a wide space occupied by blood. The lower 

 edge of the band is in the central line of the ventral side of the 

 heart, whence it rises like a longitudinal partition, its upper 



