74 Journal of Comparative Neurology. 



cu. — cuticula. o, cep/i. p. — posterior cephalic organ. 



cu^. — outer layer of cuticula. or. s. — diffuse sense-organs. 



cu'^. — inner layer of cuticula. or. sp. — special organ. 



cu. a. — modified cuticular area. /(z/. — palp. 



e. — eye. pnr. — parapodiuru. 



/. nv. — nerve-fiber. pcrs. — peristome. 



/. s. — sensory fiber. pig. — pigment granules. 



gr. inter. — intersegmental groove. pr. das. — basal process. 



k. s. — sensory hair. pr. cen. — central process. 



m.bas. — basement membrane. /;-. /^r. —peripheral process. 



in. cu. — ^perforated cuticular membrane./wJ. — prostomium. 



Viet. — metamere. p.s. — sensory pore. 



n. — nucleus. t. cen. — central tube. 



nv. — nerve. ten. — tentacle. 



0. ceph. a. — anterior cephalic organ. 



DESCRIPTION OF PLATE I. 



The drawings were made in ink and were reduced slightly more than one- 

 half linear in the plate. 



Fig. I. The diffuse sense-organs in a cephalic cirrus as shown in a longi- 

 tudinal section. Only the organs on one side of the axial nerve are shown. The 

 base of the cirrus is toward the left. From a methylene blue section restained 

 by alum cochineal. (The outlines were made with the Zeiss projection appar- 

 atus, obj. 35 mm., no ocular). 



Fig. 2. Two diffuse sense-organs whose cell-bodies lie in one group. From 

 an optical section of a living, unstained cephalic cirrus. 



Fig. 3. Epidermal cavity and normal sense-hairs of a diffuse sense-organ 

 in a cephalic cirrus. From an optical section of living, unstained material. 



Fig. 4. Epidermal cavity and abnormal sense-hairs and peripheral processes 

 of a diffuse sense-organ in a cephalic cirrus. An optical section from dying 

 material injected with methylene blue. 



Fig. J A. A longitudinal section of the modified cuticular area of a diffuse 

 sense-organ in a cephalic cirrus. From a methylene blue section restained by 

 alum cochineal. 



Fig, ^B. A longitudinal section of the modified cuticular area and periph- 

 eral processes from a diffuse sense-organ iu a ventral parapodial cirrus. From 

 a methylene blue section restained by alum cochineal. 



Fig. 6. A surface view of the modified cuticular area belonging to a dif- 

 fuse sense-organ in the cephalic cirri. From a surface view of the removed 

 cuticula. 



Fig. 7. A longitudinal section through the base of a dorsal parapodial 

 cirrus showing apparently isolated sense-cells. From a methylene blue section 

 restained by alum cochineal. A sense-cell which was unstained by the blue is 

 shown at the right. 



Fig. 8. A surface view of the modified cuticular area of a diffuse sense 

 organ in retractile tips of the palps. From a surface view of the removed 

 cuticula. 



Fig. g. A longitudinal section of the modified cuticular area of a diffuse 

 sense-organ in the peristome. The portions of the peripheral processes in 



