232 LANG DON. 



DESCRIPTION OF PLATE XIII. 



All the work was done with Zeiss apochromatic lenses. The figures were 

 drawn to a scale of 9 mm. for .01 mm. and reduced one-half in the plate. Except 

 where noted, they are from camera outlines with compens. ocular No. 8 aiid 

 obj. 4 mm.; the details were filled in with the 2 mm. oil immersion. All the figures 

 except I, 2, and 4 are from silver nitrate preparations. 



Fig. I. A sense-organ from a cross section of an anterior metamere, haema- 

 toxylin preparation. The sense-hairs are retracted. In the circular muscle-layer 

 is seen an epidermal nerve and a characteristic loop of a blood-vessel. It was 

 impossible to distinguish all structures in lower right side of figure. 



Fig. 2. A sense-organ from the buccal cavity, haeni. prep. This shows the 

 depression in the cuticula around the border of the summit of the sense-organ. 



Fig. 3. Part of the epidermis from a cross section, showing the appearance of 

 the sense-organs when unstained ; the connection of the intraepidermal nerve- 

 fibres with the subepidermal network and of this network with the efferent fibres 

 is also shown. Some of the basal processes of supporting cells were made lighter 

 to show the nerve-fibres passing across them. 



Fig. 4. A bit of the removed cuticula showing the two layers of cuticular 

 fibres, the gland-pores, and a cuticular spot over a sense-organ. The minute 

 openings in the latter are the outer openings of the pore-canals of the sense-hairs. 



Figs. 5 and 6. Intraepidermal nerve-fibres among the gland-cells of a caudal 

 metamere. The subepidermal network obscures the basement-membrane. In 

 Fig. 6, the cuticula was absent and a heavy black deposit of silver took its place. 



Fig. 7. Ends of intraepidermal nerve-fibres of the buccal cavity. Cuticula 

 absent in a and b. 



Figs. 8 and 9. Surface view of the subepidermal network from sections which 

 passed through the epidermis tangent to the basement-membrane. In Fig. 8 the 

 fibres merely cross each other. In Fig. 9 they anastomose at the part marked n. 



Fig. 10. Intraepidermal nerve-fibres and an unstained sense-organ in the 

 epithelium lining the buccal cavity. The cuticula was absent and the basement- 

 membrane could not be distinguished. Several efferent nerve-fibres and two blood- 

 vessels traverse the circular muscles. 



Figs. 11-14. Sense-organs of the median zone from cross sections of an an- 

 terior metamere. The plump, rounded form and bright brown color of the sense- 

 cells could not be represented in the.se illustrations. The section passed somewhat 

 obliquely through the organs, so that the bases of some cells are cut off and the 

 cuticula appears wider than is normal. A silver deposit beneath the cuticula adds 

 to the apparent width of the latter. In Figs. 11 and 12 the connection of a sen- 

 sory fibre with its sense-cell is shown. 



Fig. 15. Bases of sense-cells from oblique sections of the sense-organs of the 

 ventral surface of the prostomium. The summits of the cells have been cut off. 



