POLYCH^ETA SEDENTARIA OF THE FIRTH OF FORTH. 645 



In both the branchiae and the tentacles there are nerves. In either case 

 these are seen in a prepared section as a pair of fibrillar strands situated in the 

 deeper region of the epidermis, and running longitudinally. In the branchia 

 the two nerves are at opposite sides of the filament ; in the tentacles they are 

 placed one on each side of the groove (PI. XXXIX. figs. 9 d, 9 v). 



The nerve cords in the body are not separated from the epidermis, though 

 they are defined with considerable distinctness. The fibrillar portion of the 

 cords does not stain in borax carmine. There is no differentiation of ganglia, 

 the nerve cells being distributed uniformly along the ventral side of the cords. 



The dorsal vessel in this and all other species of Cirratulus has a very peculiar 

 structure, which has been described by Claparede.* By examining the living 

 animal under a low power, the dorsal vessel can be seen to contain a bright 

 red liquid, and to be bordered by three black granular-looking cords, one 

 dorsal and two lateral. The vessel is much constricted where it passes 

 through the mesenteries, and much enlarged in the body of the somite. It 

 also has a very tortuous course when the animal is in an average state of con- 

 traction. Claparede studied the vessel in Andouinia Jiligera ( = C. tentacu- 

 latus), and states that the wall is formed by a muscular tunic formed of 

 annular fibres, within which the " cordons bruns " are placed. He was unable 

 to decide whether these cords were between the muscular tunic and the 

 vessel's own wall, or within the latter. Our sections show clearly the relations 

 of the cords, and also their minute structure, on which Claparede says nothing. 

 It should have been mentioned that the dorsal cord is often interrupted, and 

 occasionally coalesces with one of the lateral. The cords are in the interior 

 of the vessel, and although they are usually in contact with the inner surface 

 of the wall, they are not continuous Avith it : the pseudhsemal fluid is frequently 

 seen in the sections between one of the cords and the wall of the vessel. The 

 structure of the cords is very peculiar : it has a glandular character, but it is 

 difficult to decide whether the organs have a glandular function, as they have 

 neither lumen nor efferent duct, nor have we been able to trace any connection 

 between them and any other organ of the body. The cords are composed of 

 elongated cells placed perpendicularly to the interior of the cord, which is 

 enclosed by an extremely thin basement membrane. In our sections the cells 

 are not stained. They contain a number of minute rounded granules similar 

 to those which are seen in the secreting cells of nephridia in several Chaetopoda, 

 and also somewhat similar to granules in the secretory cells of the epithelium 

 of the intestine. These granules are in greatest abundance towards the 

 external parts of the cells. 



The dorsal vessel gives off on each side a large vessel in the 3rd somite, 

 the branch passes backwards and forms a lateral vessel, from which the 



* Chetopodes du Golfe de Naples, Geneve, 1868. 



