1902.] On the Gastric Organs of Spirula, Nautilus, etc. 233 



which, curiously enough, like Nassopsis, are members of the old marine 

 fauna of Lake Tanganyika, and it also occurs in the genus Turritella.* 



It has often been stated that the crystalline style, and in consequence 

 presumably its sac, occurs generally among the Rhipidoglossa, but so 

 far as we have been able to ascertain, this is not the case ; at any rate, the 

 style-sac does not occur in Pleurotomaria, Trochus, Turbo, or Haliotis. 



Nassopsis thus presents us with a stomach in which these appendages 

 are more completely developed than in the Ehipidoglossa, and in this 

 genus the gastric apparatus has the following relationships : — 



The oesophagus leads into the stomach in the manner represented in 

 fig. 1, as. In the gastric chamber into which it opens there are several 

 conspicuous glandular folds, and two of these (s.f.) which lead away 

 from the oesophageal aperture contain between them the opening of a 

 conspicuous "bile duct" (Id.). As they recede from the oesophageal 

 aperture they approximate together and become related to a complex 

 spiral organ (sp. c.) which projects beyond the parietes of the stomach 

 and constitutes the so-called spiral caecum. At the opposite end of 

 the stomach and constricted off from it by a raised annulus, there is 

 another thick-walled diverticulum which is lined with a shining cuti- 

 cular membrane ; this is the style-sac, and in Nassopsis it generally 

 contains a semi-transparent mass of secretion, the so-called crystalline 

 style (fig. 1, c.s.). Thus of such a stomach it may be said that the 

 intestinal and oesophageal apertures are related to a proper stomachic 

 chamber which possesses two chief diverticula, on the one hand the 

 style-sac, and on the other a complex spiral organ in definite relation 

 to the principal bile duct, the spiral csecum. 



It has generally been assumed that the gastric apparatus of a 

 Cephalop'od differs from, and is more complex than, that of the Gastro- 

 pods. But keeping the above condition of the gastric apparatus in 

 Nassopsis in mind, we find that in Nautilus (fig. 2, or in Sepia, fig. 3) 

 the oesophagus after becoming dilated into an expansion known 

 as the " crop " (fig. 2, c.r.), leads into a narrow folded tube (s.t.). This 

 tubular portion is connected with a diverticulum, the so-called "gizzard" 

 (c.s.) of the Cephalopods, but which like the crystalline style-sac of the 

 Gastropods has thick walls, and is lined inside by a folded cuticular 

 membrane (cm.). In Nautilus, moreover, the so-called gizzard is con- 

 stricted off from the stomach proper by a thickened annulus, corre- 

 sponding to that which separates the style-sac of the Gastropods from 

 the stomach proper. The gizzard of Nautilus is in fact a diverticulum 

 of the stomach, and has exactly the same general structure as the 

 style-sac in Nassopsis. 



* W. B. Randies, < Anat. Anz.,' 1902. Ed. xxi, p. 201. 



With the exception of Turritella communis, both style-sac and caecum have 

 hitherto only been found in association in the stomachs of the Halolimnic Gastro- 

 pods of Tanganyika. 



