PEAELY NAUTILUS. 341 



Spengel's Olfactory Organ. 



The extremely important observations of Spengel on the 

 olfactory organ of Mollusca (' Zeitsch. wiss. Zoologie/ vol. 

 35) lead to the conclusion that there is very generally if not 

 universally present in the Mollusca an olfactory organ placed 

 near to or in relation with each gill, and that this organ 

 receives its nerve from the " visceral loop" or commissure, 

 which, sometimes short, sometimes long, in some molluscs 

 twisted, in others straight, joins to one another the pair of 

 so-called " visceral" ganglia. 



We adopt the name " osphradium" for this molluscan organ 

 of smell, proposed by Professor Lankester in his article " Mol- 

 lusca," in the ' Encyclopaedia Britannica.' The osphradium is 

 thus distinguished by its name from all other organs presumed 

 to have the olfactory function, whether placed on the head; 

 lips, tentacles, or elsewhere. The osphradium of molluscs is 

 Spengel's olfactory organ, it lies near the gill and tests the 

 respiratory medium. 



Spengel was unable to find an osphradium in Cephalopoda. 

 He appears not to have had the opportunity of examining 

 Nautilus, where a well-developed pair of osphradia exist, 

 although we have not been able to detect their representatives 

 in Sepia or Octopus. 



The osphradia of Nautilus are in the form of a pair of teat- 

 like papillae placed upon the body- wall of the subpallial chamber, 

 a little to the outer side of the muscular attachments of the an- 

 terior pair of gills, one corresponding to the right gill and the 

 other to the left gill (woodcut, figs, 1, 2, olf.). 



These papillae have been seen and figured by previous 

 writers (Van der Hoeven, Keferstein), but no suggestion as to 

 their significance has ever been made. We were led to infer 

 from their position that they represented Spengel's olfactory 

 organ, and proceeded to test that hypothesis by an examination, 

 firstly, of their microscopic structure, and secondly, of their 

 nerve-supply. 



The inquiry into their microscopic structure was entirely 

 negative. Our specimens were not sufficiently well preserved 



VOL. XXIII. NEW SEH. Z 



