60 Prof. J. Van der Hoeven on the Anatomy 



form varies in the two sexes, was the more interesting, since the 

 Nautilus differs in so many respects from all other cephalopoda 

 which belong to the present history of the earth, and finds its 

 nearest affinities alone in fossil species of its own genus and of 

 the numerous families of the Ammonites, an extinct group be- 

 longing to periods long passed away. Some years ago I hap- 

 pened to become possessed of a male specimen of this animal 

 species, which however was in such a mutilated condition as to 

 render the investigation of the internal parts impossible. Such 

 deviations as I observed in the external parts of this specimen 

 might still, however, be the result of occasional malformation, 

 likely perhaps to occur in an equal degree in a female individual. 

 In the description therefore which I gave of this specimen in 

 the 'Instituut van Wetenschappen, Letterkunde en schoone 

 Kunsten*,^ I chose to abstain from a decided opinion, and to leave 

 it undetermined whether there was here an individual modifica- 

 tion of form or really a normal sexual difference. I advanced 

 the latter as a surmise, which however appeared to be highly 

 probable when, amongst the still increasing number of specimens 

 brought to Europe, the same or similar deviations of form had 

 not been observed. 



From the year 1827, when I investigated this specimen, my 

 attention was constantly directed to this point, and I am now in 

 a condition to determine the question with full certainty. In 

 the spring of 1855 I received, through the courtesy of his Excel- 

 lency the Governor-General of the Dutch Indies, certain speci- 

 mens of Nautilus, amongst which were several males in various 

 states of preservation ; and although all of them were thus not well 

 adapted for the investigation of the internal organs, they never- 

 theless presented all the external parts uninjured, and agreed in 

 the most minute particulars with the specimen examined in 

 1847. 



Consequently I am no longer satisfied with a surmise, but am 

 able to assert with perfect certainty, that in the external parts in 

 the two sexes of Nautilus Pompilius a remarkable and constant 

 difference prevails. To state clearly in what this difference con- 



* 1848, bl. 67-73, pi. 1. figs. 1-3. These observations were after- 

 wards published in the Trans, of the Zool. Society, vol. iv. part i. London 

 1851, pp. 21-29, pi. 5-8, under the title of " Contiiljutions to the knowledge 

 of the Animal of Nautilus Pompilius." 



With respect to a peculiarity there announced, that in the spaces which 

 the follicular appendages of the anterior branchial artery enclose, I had 

 found a stony concrement, I may remark, that the same thing occurred to 

 me afterwards in another specimen. The ossicle, investigated by Dr. L. C. 

 Levoir at my request, weighed 0*47 grain (dried 0-438) ; had a spec. gr. of 

 1"66 ; it contained some traces of albumen, but no uric acid ; and 70*4 per 

 cent, of inorganic matter, principally neutral phosphate of lime. 



