Lang DON, Sense-organs of Nereis virens. 45 



plicated epidermal organs to which I have given the name 

 spiral organs because of the peculiar spiral arrangement of the 

 peripheral processes of their cells. I have found these organs 

 not only in Nereis virens, but also in the living parapodia of a 

 second species — probably N, limbata, Ehlers. 



A. Structure . 



Each organ consists of a slender central tube around which 

 are the spirally arranged peripheral processes from about 100 bi- 

 polar or multipolar cells whose bodies generally lie in the epider- 

 mis (Plate II, Fig. 41). The central tube and the peripheral 

 processes arranged around it, whether seen in living material or 

 in sections, form the most conspicuous part of one of these 

 organs. This part is nearly ovoid, about 80 jx long, 40 /x wide 

 at its widest part, and has its smaller, somewhat pointed end 

 pressed into a small cavity in the under side of the cuticula. 

 This cavity is about 6 fi wide at the inner limit of the cuticula ; 

 from it a tubular opening or canal about 2 // in dirmeter extends 

 entirely through the cuticula, flaring a little at its outer end at 

 which it becomes 4 y^ in diameter (Plate II, Figs. 44 and 47). 



The central tube is a cylindrical, flexible, thin-walled struc- 

 ture ; it enlarges gradually from its peripheral to to its central 

 end and averages 2 m in diameter (Fig. 43). The basal end of 

 this tube appears to end blindly, but it is so covered by the 

 lowest peripheral processes that it is difficult to determine this 

 with certainty. The peripheral end of the tube passes into the 

 shallow cavity in the under side of this cuticula above it. In the 

 body epidermis and in the bases of the palps, the apical turn of 

 the spiral formed by the peripheral processes lies in this cavity 

 in the under side of the cuticula just where the cavity passes into 

 the cuticular canal above it (Fig. 41.) In the gill lobes, the 

 cuticula is very much thinner ; in this region the apical turn of 

 the spiral lies entirely below the cuticula and it can be seen that 

 the central tube runs up to the cuticular canal and that the 

 lumen of the tube is continuous with that of the canal and 

 therefore opens to the exterior (Plate II, Fig. 43). 



Quite often one of these cuticular canals contains a rod-like 



