Langdon, Scfise-organs of Nereis virens. 21 



TJie diffuse sense-orgatis of the anal citri as seen in haema- 

 toxylin preparations are exactly like those of the cephalic cirri. 

 Owing to the fact that the caudal end is broken off by the contor- 

 tions of the worm when injected it is difficult to obtain methy- 

 lene blue preparations of this region. 



In the tentacles and the retractile tips of the palps the sensory 

 cells are also grouped into definite sense-organs which are prac- 

 tically like those of the cephalic cirri. Because of the smaller 

 size, however, of the tentacles and palps, their sense-organs 

 have less room and the sensory cells are, therefore, crowded 

 toward the median axis of each appendage, thus giving rise to 

 what appears to be a crowded mass of isolated cells. It can be 

 seen, however, that each modified cuticular area is supplied by 

 peripheral processes from several sensory cells, thus plainly 

 showing the grouping of these cells into definite organs (Plate 

 I, Figs. 14 and 15.) 



In sections of the palp, it is a little more difficult to locate 

 a bundle of peripheral processes in its cavity among the bodies 

 of the epidermal cells because the latter, instead of stiffly out- 

 lining this cavity as in the cephalic cirri, press closely against 

 the bundle of processes (Plate I, Fig. 15). The modified cuti- 

 cular area over a sense-organ in this region, as seen in sections, 

 differs from that of the cephalic cirri in but one point — the inner 

 cuticular layer is thinner in the palps thus rendering the con- 

 cavity beneath the perforated membrane more shallow than in 

 the cirri. A surface view of this cuticular area presents several 

 differences. The pores through which the sensory hairs pass are 

 smaller and more numerous — varying from 8 to 21 in number — 

 and they form an almost circular group. 



Each of these groups is in some preparations of the removed cuticula sur- 

 rounded by a number of larger pores which resemble gland pores (Plate I, Fig. 

 8). Sections through the palps, however, show that not only are there no glands 

 whatever in the tips of the palps but that there are no canals in the cuticula 

 aside from those through which the sensory hairs pass — i. e., those which lead 

 to the central group of minute pores seen in a surface view. A discussion of 

 these larger pores will be left until the anchoring cells found in the epidermis 

 are described. 



