POLYCH^ETA. SEDENTARIA OF THE FIRTH OF FORTH. 675 



heart of the anterior region, the dorsal vessel of other annelids being repre- 

 sented by the blood-sinus in the wall of the intestine. Horst, therefore, 

 asserted that the Chlorhaemidse possessed the same relations in the pseudhsemal 

 vessel as the Enchytrseidse according to the researches of Vejdovsky. The 

 view which seems to us the true one to take of the condition of things found 

 in Trophonia is as follows : — Behind the loop of the intestine there is a series 

 of vessels passing from the intestinal walls to the dorsal trunk. The dorsal 

 vessel is to be regarded as continued by that part of the heart which is in 

 front of the point where the dorsal vessel joins it. The part behind this 

 represents (enormously enlarged) simply the vessels connecting the looped 

 part of the intestine with the dorsal vessel. It is probable that the loop of 

 the intestine corresponds to just two somites, for there are two vessels passing 

 from the ventral vessel to the loop : the posterior part of the heart corres- 

 ponds to two corresponding dorsal communicating vessels. 



The meaning of the glandular body contained in the heart is difficult to 

 surmise. Horst considers it to have been originally derived from the 

 intestinal epithelium. We have found that in the adult Trophonia the cardiac 

 body is entirely separate from the intestine, although at the posterior end of 

 the heart the glandular body and the intestinal body-wall are in extremely 

 close contact. The continuity of the blood-sinuses in the intestinal wall 

 with those of the heart is obvious enough in sections. The minute structure 

 of the cardiac body is closely similar to that of a nephridium. The whole 

 organ or gland consists of a number of tubes having for the most part a 

 longitudinal direction ; some of these tubes have a lumen, the walls being 

 lined with transparent nucleated cells containing granules, while in other tubes 

 similar cells completely fill the cavity. (See Cunningham, " Some Points in 

 the Anatomy of Polychseta," Quart. Jour. Micr. Sci, 1887.) 



There is only a single pair of nephridia placed longitudinally in the head. 

 They extend posteriorly as far as the 6th to 8th somite. In colour they are 

 yellowish green or white to the naked eye. They open anteriorly on the 

 invaginated first somite at the side of the tentacles. We have not been able to 

 discover any ccelomic opening or nephrostome. 



When a piece of the nephridium is taken in the fresh condition and 

 slightly teased in a drop of sea water, the whole structure of the glandular 

 epithelium is beautifully seen. Scattered all over the field of the microscope 

 are seen globular gelatinous-looking bodies, each with a slight globular con- 

 cretion at its centre. In places a number of these gelatinous globules are 

 seen united together : there are also spherical cells with delicate walls, each 

 containing 10 or 12 of the globules. Again, there are a number of smaller 

 cells, each containing several of the black concretions of smaller or larger size, 

 and each cell bearing a single large cilium or flagellum, vibrating either very 



VOL. XXXIII. PART III. 5 F 



