792 MECHANISM OF RESPIRATION, ETC. 



seconde paii-e d'osphradies fusionn^es [Willey] ne parait done pas soutenable." Dr Pel- 

 seneer makes no reference to my discovery of cilia' on the osphradia, otherwise he could 

 hardly have been so categorical as to the absence of a " region sensorielle." 



Continued investigation of the organs by finer methods than I had previously employed 

 has resulted in a confirmation of my interpretation (PI. LXXXIII. figg. 3 — 8). Even 

 without this confirmation I should have confidently adhered to the view expressed upon 

 grounds of topography, homodynamy, and ciliation of protected surfaces, and I gather that 

 this view has found favour with Dr Ludwig Plate-. 



The two paii-s of osphradia may be distinguished as the interbranchial osphradia and 

 the suhmedian^ osphradia respectively. The nerves which supply the former are not difficult 

 to find in section, and they have been figured in longitudinal section, i.e. in a section 

 parallel to the sagittal plane of the body, by Pelseneer (op. cit. PI. xxi. fig. 180). 

 Pelseneer says that the papilla is not sensory, but only the subjacent pallial epithelium, 

 which receives " un grand nombre de ramifications d'un filet du nerf visceral-branchial." 

 I am able to confirm this statement, with the reservation that I find that the sensory 

 epithelium is not confined to the adjacent pallial surface, but extends round the angle of 

 insertion of the papilla (PI. LXXXIII. fig. 7). 



In the case of the submedian osphradia the entire sensory epithelium is raised above 

 the level of the pallial surface while maintaining its character as a sensory groove, for 

 protective purposes no doubt, and so it comes about that the papillae are bilobate with 

 the sensory surface occupying the depression between the lobes in each case. The nerves 

 are best seen in sections taken parallel to the long axis of the body, and in such sections, 

 if properly prepared, the nerves may be found to penetrate through the basement-membrane 

 of the epidermis, and to spread out in the substance of the latter external to the base- 

 ment-membrane (PL LXXXIII. figg. 3 — 8). In this way a remarkable intra-epidermal 

 fihi-iUar plexus is brought into existence comparable for example with the intra-epidermal 

 terminations of the collar nerve-roots of the Enteropneusta^ What is more to the point 

 however is that an exactly similar intra-epidetmal distribution of nerve-fibres in the osphradia 

 was described by Professor SpengeP in 1881 in the case of the primitive Lamellibranch 

 Area noae as well as in the Prosobranchs Haliutis and Trochus. The identity of distri- 

 bution of nerves in the osphradia of these Molluscs and of Naidilus may be said to be 

 demonstrative. 



According to Professor Spengel's account, the osphradium of Area resembles that of 

 Haliotis and of Trochus in that from the subjacent visceral ganglion numerous nerves arise 

 which enter the pigmented cylinder-epithelium and distribute themselves in this "so dass 

 wir dasselbe eigenthtimliche Bild einen von starken Nervenfaserstrangen durchbrochenen 

 Ejjithelschicht vor uns haben wie dort." 



' Willey, A., " The pre-ocular and post-ooular tentacles and osphradia of Nautilus." Quart. J. Micr. Sc. 

 Vol. 40, 1897, pp. 197—201, PI. x. 



^ Plate, H. L., "Die Anatomie und Phylogenie der Chitonen." Fortsetzung Fauna Chilensis, Part C. 

 Zool. Jahrb., Supplement v. Bd. n. 1901, p. 561. 



' The epithet "post-anal" in this connection is wrong both in substance and in fact. 



•• Cf. Zool. Res., Part in. 1899, especially the case of Pttfchodera caritosa, p. 2-52. 



'■ Spengel, J. W., " Die Geruchsorgane und das Nervensystem der MoUusken. Bin Beitrag zur Erkenntnis 

 der Einheit des MoUuskentypus." Zeitschr. wiss. Zool. Bd. 35, 1881, p. 375, Taf. sax. fig. 27. 



