DIGITAL AND OPHTHALMIC TENTACLES. 779 



Homologies of In/rabuccal Organ of Male and Female Nautilus. 



Male. Female. 



Lamelligerous lobes Tentaculiferous lobes 

 Peduncle Lamelligerous lobe 



I cannot say with certainty whether the innervation of the infrabuccal apparatus 

 of male and female affords conclusive evidence of the truth of the above comparisons, 

 but I think it may. 



The first accurate account of the innervation of the female infrabuccal organ was 

 furnished by Mr Graham Ken- in 189.5'. A single nerve-trunk, the last to leave the 

 pedal ganglion, external to the infundibular nerve (PL LXXXII. figg. 4 and 5) crosses 

 the peristomial haemocoel on each side, and penetrates into the base of the infi-abuccal 

 organ. " This bends towards the middle line, pursues a curved couree in the substance of 

 the lobe, and meets with its fellow of the opposite side " (Kerr, op. cit, p. 676). From 

 this commissural nerve, which I propose to call after its discoverer, Kerr's collector 

 or commissure, branches are given off which pass directly to the tentacles and lamellae 

 individually. I have dissected out this remarkable nerve in the female infrabuccal organ, 

 but in the male I have been unable to trace a connection between the right and left 

 infrabuccal nerves, the median portion of the nerve from which, in the female, the branches 

 to the lamellae arise, apparently not occurring in the male (PI. LXXXII. figg. 1 and 2). 



Finally it may be remarked that the infrabuccal apparatus of Nautilus in general 

 combines the properties of gland and sense-organ, but that it is in any case an accessory 

 sexual organ since it differs in male and female. It is therefore not appropriate to 

 ascribe an olfactory function to it, since this e.xpression is too precise in the present 

 state of our knowledge and moreover leads to confusion with the true rhinophore^ and 

 the ophthalmic tentacles which present no sexual differences. 



There is another lamellar organ in the female to which I have already referred, 

 which occupies the inner surface of what I have called the ventral symphysial tract. 

 It is composed of two halves separated in the middle line, and the lamellae of each 

 half are disposed in an arcuate manner, running at first longitudinally, and then curving 

 inwards or transversely to the middle line. 



This organ was first correctly described by Valenciennes^, and I shall call it the 

 Organ of Valenciennes, in order to distinguish it from the infrabuccal lamellar organ of 

 the female which is the Organ of Owen, and from the infrabuccal lamellar organ of 

 the male which is the Organ of Van der Hoeven. 



The median division which separa,tes the two halves of the organ of Valenciennes 

 is not always very distinct, and Kerr'' has figured an example in which the lamellae 



' Kerr, J. G., op. cit., P. Zool. Soc. London, 1895, p. 675. 



'' Owen (1832) surmised that the lamellae of the female infrabuccal organ exercised an olfactory function, 

 in ignorance of the sexual differences which were first made known by Van der Hoeven (1850) and in 

 ignorance of the rhinophore which was discovered by Valenciennes (1841). 



^ Valenciennes, A., op. cit. 1841, p. 277, PI. xi. fig. 1 (. 



* Kerr, J. G., op. cit. 1895, P. Zool. Soc. PI. xxxix. I have also observed that some of the lamellae 

 may become confluent across the middle line, while others in the same organ remain distinct on each side. 



w. VI. 102 



