76 Journal of Comparative Neurology. 



Fig. 26. Four views of a single sense-hair of a diffuse sense-organ show- 

 ing successive stages in the withdrawal of a hair which has its apex already 

 swollen into a ball. From a dying parapodial cirrus. 



Fig. 2y. The normal sense-hairs of three diffuse sense-organs situated in 

 the dorsal border of a dorsal parapodial cirrus. From living, unstained material. 



Fig. 28. A diagram showing the distribution of the spiral organs as far 

 back as the first raetamere. A wax model was constructed from sections and 

 the position of each spiral organ marked on the surface. Tissue paper was then 

 carefully fitted over the surface of the left half of the model and the position 

 of each organ, as seen through the tissue paper, was marked in pencil on the 

 latter. The tissue paper was then straightened and the chart thus obtained 

 transfered to drawing paper. The right hand margin of the figure represents 

 the mid-dorsal line and the left one the mid-ventral line. The position of the 

 spiral organs is shown by the black dots. The broken lines mark the position 

 of grooves in the surface. 



Fig. 2g. The cell-bodies and a few of the peripheral processes of one of 

 the anterior cephalic organs as seen in a longitudinal section of the prostomium. 

 From methylene blue material restained by alum cochineal. 



DESCRIPTION OF PLATE II. 



Figs. JO-J2. Longitudinal sections of diffuse sense-organs in the peristome. 

 The sensory hairs were mostly withdrawn. Fig. 30 shows the connection of a 

 central process with an epidermal nerve and Fig. 32 shows an organ in which but 

 one of the nerve cells has taken the blue. From methylene blue material re- 

 stained with alum cochineal. 



Fig. jj. Optical view of a diffuse sense-organ in a cephaiic cirrus. The 

 under side of the perforated membrane is shown. From living, methylene blue 

 material. 



Fig, j^. A longitudinal section of the modified cuticular cavity of a dif- 

 fuse sense-organ in the peristome. One sense-hair retains its normal position. 

 The rest have been withdrawn into the inner cuticular cavity. From methylene 

 blue material restained by alum cochineal. 



Fig. jj. A single nerve cell belonging to a diffuse sense-organ in the ceph- 

 alic cirri. The peripheral process of this cell has four branches. Varicosities 

 have formed at the tips of the sensory hairs and one large one in the peripheral 

 process itself. P>om dying, methylene blue material. 



Fig. 36. An optical longitudinal section through the tip of a cephalic 

 cirrus. The sense-hairs belonging to two diffuse sense-organs are shown and one 

 peripheral process which took the blue and which has a large varicosity. From 

 dying, methylene blue material. 



Fig. jp'. An oblique section of a modified cuticular area of a diffuse sense- 

 organ. The outer cuticular cavity does not appear in this section. One periph- 

 eral process branches in the inner cuticular cavity. From methylene blue ma- 

 terial restained by alum cochineal. 



Fig. j8. Optical view of the peripheral processes of the di ffuse sense-organs 

 whose cells lie in a single group. The perforated membranes are shown from 

 underneath. From a living cephalic cirrus stained by methylene blue. 



