824 DESCRIPTION OF PLATES. 



acetic acid and alum cochineal the nucleus presents a chromatic reticulum. Zeiss Oc. 3, Obj. J, 

 water imm., Cam. luc. 



Fig. 2. Otocones. Zeiss 3 J, Cam. luc. 



Fig. 3. Sagittal section (parallel to long axis of body) through one of the submedian 

 osphradia. Only the epidermis and nerves are drawn. The limits of the sensory epithelium 

 are indicated by slight elevations near the borders of the figure. A large nerve proceeding 

 through the conjunctive framework from below is seen to branch and then penetrate through 

 the basement-membrane into the substance of the epidermis, where it terminates in an intra- 

 epidermal fibrillar plexus. Zeiss 3 A. 



b.in. Basement-membrane. 



n. Nerves with subcutaneous and intra-epidermal course. 



Fig. 4. Portion of a similar section more highly magnified, showing a remarkable intra- 

 epidermal fibrillar plexus. Zeiss 3 D, Cam. luc. 



Fig. 5. Tangential section through the epidermis of a submedian osphradium taken 

 through one of tlie angles made by the papilliform lobes (which arch over and protect the 

 sensory surface of each submedian osphradium) with the base of the osphradial groove. The 

 ramifying intra-epidermal fibrillar plexus is well shown, and there are also indications of the 

 occurrence of peripheral ganglion-cells. Zeiss 3 C, Cam. luc. 



Fig. 6. Papilla of an interbranchial osphradium showing cilia. Drawn from the living 

 object and reproduced from Quart. J. Micr. Sc, 1897. 



Fig. 7. Section through an interbranchial osphradium cutting the papilla lengthwise, 

 i.e. at right angles to the long axis of the body, showing the papilla itself and the subjacent 

 surface of the mantle. The sensory surface occupies a well-defined tract about the angle 

 made by the papilla with the mantle. Cilia not shown in the drawing. 



o.p. Apex of the osphradial papilla. 



n. Subcutaneous and intra-epidermal nerves. 



Fig. 8. Enlarged view of the intra-epidermal termination of a nerve (n.) in an inter- 

 branchial osphradium. 



Fig. 9. Transverse section through the siphuncle showing the central sinus (siphuncular 

 vein) and peripheral lacunae communicating with it. 



a. Main artery of the siphuncle. 



d. and v. Dorsal and ventral surfaces of the siphuncle. 



Fig. 10. Portion of the wall of the siphuncle showing the intra-epidermal prolongations 

 of the subcutaneous lacunae. Zeiss 2 D, Cam. luc. 



s. Subcutaneous blood-spaces or lacunae. 



t. Trabeculae. 



Fig. II. Longitudinal section through siphuncle, showing the axial vein oommunicatLng 

 with the peripheral lacunae. 



«. Axial sinus or vein ; (the index lines pointing to the sides of the sinus should not 

 have been inserted). 



Fig. 12. Portion of wall of preceding, showing the longitudinal course of one of the 

 intra-epidermal blood-channels. 

 s. Venous space. 



