Langdon, Sense-organs of Nereis virens. yy 



Figs. 3g and ^o. Apparent pericellular nerve-baskets around ganglion cells 

 in a cirrus ganglion. Fig. 39 shows the position of this basket in relation to 

 both the ganglion cell and its capsule. The protoplasm of the cell has shrunken. 

 Fig. 40 shows the centripetal nerve-fiber around the axis-cylinder of the gan- 

 glion cell. From sections of methylene blue material restained by alum cochineal. 



Fig. ^i. A longitudinal section of a spiral organ in the peristome. From 

 material killed in Miiller's fluid and stained with Kleinenberg's hsematoxylin. 



Figs. 42 and 43. Optical sections of parts of two spiral organs in the gill 

 lobes. In Fig. 43 the whole of the central tube and a surface view of its ex- 

 ternal opening is shown. Fig. 42 shows the base of an organ. From living, 

 unstained material. 



Figs. 44 and 4^. Two abnormal appearances sometimes seen in longitudi- 

 nal sections of the outer ends of spiral organs, appearance apparently due to the 

 central tube contracting away from the surrounding cuticula. From material 

 killed in Miiller's fluid and stained with Kleinenberg's haematoxylin. 



Fig. 46. A lateral view of a tip of one of the peripheral processes belong- 

 ing to a spiral organ. In this tip only the apical block of the refractive body 

 ould be seen (see Text-figure 4). From material killed with alcohol and stained 

 with Kleinenberg's hematoxylin. 



Fig. 4y. An optical section of the summit of a spiral organ showing the 

 apical turn of the spirally arranged peripheral processes. The cuticula is shown 

 in surface view. From living, unstained gill lobes. 



Fig. 48. Several peripheral processes containing abnormal or accessory 

 refractive bodies. From spiral organs in living, unstained gill lobes. 



Fig. 4g. Two of the epidermal anchoring cells as seen in a longitudinal 

 view of the peristome. From methylene blue material restained with alum 

 cochineal. 



DESCRIPTION OF PLATE III. 



This chart was made from the removed cuticula by means of the Zeiss pro- 

 jection apparatus fitted with obj. 35 mm. and no eye piece. It was drawn to a 

 scale of I dm. for 2 mm. and has been much reduced in the plate. 



Fig. 50. A chart showing the distribution of the diffuse sense-organs. 

 This chart is from one half the cuticula extending from the mid-dorsal line 

 to the mid-ventral line. The metameres are separated by heavy black lines 

 which represent the intersegmental grooves; other grooves are shown by broken 

 lines. The small black dots represent the cuticular areas over the sense-organs. 



Fig. 57. The arrangement of the modified cuticular areas belonging to 

 the diffuse sense-organs as shown in a bit of the cuticula from near the base of a 

 cirrus (compare with Fig. 19). 



