. Contribution to the natural history of the pearly nautilus. Nautilidae. 742 SEXUAL DIMORPHISM. The sexual dimorphism is more pronounced in Nautilus than in any other recent Cephalopod, with the exception of Argonauta, owing to the fact that the spadix is Extreme of Minimum of Difference. Fig. 2. Secondary sexual characters in shells of Nautilus pompilius. [Reproduced by favour of Dr F. A. Bather from Natural Science, Vol. vi. 1895, p. 411.] •a permanent structure, having a gradual development from the adolescent to the adult stages. It is not periodic in its appearance as is the
. Contribution to the natural history of the pearly nautilus. Nautilidae. 742 SEXUAL DIMORPHISM. The sexual dimorphism is more pronounced in Nautilus than in any other recent Cephalopod, with the exception of Argonauta, owing to the fact that the spadix is Extreme of Minimum of Difference. Fig. 2. Secondary sexual characters in shells of Nautilus pompilius. [Reproduced by favour of Dr F. A. Bather from Natural Science, Vol. vi. 1895, p. 411.] •a permanent structure, having a gradual development from the adolescent to the adult stages. It is not periodic in its appearance as is the hectocotylus of the Dibranchs. That its presence should determine a difference in the shape and dimensions of the orifice of the shell, is a fact which has already been made use of by palaeontologists, who now recognise similar sexual variations in the shells of extinct species. Commenting upon my observations and figures (published in 1895) relating to the shells of male and female Nautilus, Professor Howes1 pointed out that these and the nearly contemporaneous observations of M. Vayssiere bore out the suggestion made by D'Orbigny more than fifty years ago that certain differences in the shells of Ammonites might possibly be indicative of sexual variation. 1 Howes, G. B. Address of the President, P. Malac. Soc. London, Vol. n., 1896—1897, see pp. 69— Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Willey, Arthur, b. 1867; Willey, Arthur, b. 1867. Zoological results based on material from New Britain, New Guinea, Loyalty Islands and elsewhere, collected during the years 1895, 1896 and 1897. Pt. 6. [Cambridge, Eng. : University Press]
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