Langdon, Sense-organs of Nereis vircns. 75 



the inner cuticular cavity and the sense-hairs appear to be nearly normal. From 

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



Fig. 10. Omitted from the plate. 



Ftg. II. A surface view of the modified cuticular area of a diffuse sense- 

 organ in the body epidermis. From a surface view of the removed cuticula. 



Fig. 12. Normal shape of the bodies of the sense-cells of the diffuse sense- 

 organs in the cephalic cirri. From living unstained material. 



Figs, ij A and B. Two optical longitudinal sections of the epidermal cav- 

 ities of the diffuse sense-organs in the cephalic cirri. From living, unstained 

 material. In Fig. 13 B the position of the peripheral processes of an epidermal 

 cavity is shown. 



Fig. i^. A longitudinal section of a diffuse sense-organ in the tentacles. 

 From methylene blue material restained by alum cochineal. 



^^i- ^5- A longitudinal section of a diffuse sense-organ in the palps. From 

 methylene blue material restained by alum cochineal. 



Fig. lb. A longitudinal section through the modified cuticular area of a 

 diffuse sense-organ in the cephalic cirri. From methylene blue material re- 

 stained by alum cochineal. 



Fig. 77. A longitudinal section of a diffuse sense-organ in the base of the 

 dorsal border of a dorsal parapodial cirrus. From material killed in alcohol and 

 stained with Kleinenberg's hsematoxylin. 



Fig. 18. The outline of a longitudinal optical section of a dorsal para- 

 podial cirrus showing the arrangement of the sense-hairs in definite groups along 

 the dorsal and ventral borders and the apparently isolated ones at the tip of the 

 cirrus. From living, unstained material. 



Fig. ig. The surface view of one-half the surface of the distal part of a 

 cephalic cirrus. The location of the modified cuticular areas of the diffuse 

 sense-organs is marked by the circles over the surface and by the groups of 

 sense-hairs around the margin. The tip of the cirrus was so transparent that 

 the location of the sense organs in it could not be seen. From living, stained 

 material. 



Fig. 20. A group of sense-hairs which have become swollen into balls ' 

 resting on the cuticula. From a diffuse sense-organ in unstained dying material. 



Fig. 21. A surface view of one side of a dorsal parapodial cirrus. The 

 distribution of the modified cuticular areas of the diffuse sense-organs in the 

 surface is shown by the circles. The sense-hairs around the margin did not 

 show (see Fig. 18). A camera drawing from living stained material. 



Fig. 22. A few of the cells of a spiral organ in a gill-lobe. From an opti- 

 cal view of living material that had been injected with methylene blue. In this 

 organ only the cells shown in the figure took the blue. 



Fig. 23. The sense-hairs of the diffuse sense-organs along the dorsal border 

 of a dorsal parapodial cirrus. The hairs near the base appear to be isolated, 

 those nearer the tip appear to be arranged in groups. The base of the cirrus is 

 toward the left. From living unstained material. 



Fig. 24. Sense-hairs in diffuse sense-organs from a parapodial cirrus. Each 

 hair has its tip swollen into a little ball. From dying unstained material. 



Fig. 2^. A sense-hair which has become thickened at its base. From a 

 diffuse sense-organ in a dying parapodial cirrus. 



