26 VAN DER HOEVEN ON THE ANIMAL 



calcareous white matter, as has been observed in the first accurate description of the 

 animal by my eminent friend Professor Owen. 



The sexual difference of the Nautilus requires still further elucidation. Professor 

 Owen's description was relative to a female, and also all the other specimens observed by 

 subsequent authors, or preserved hitherto in the museums, seem to be of female speci- 

 mens. Hence it seems to follow that males are rarer ; a similar circumstance of unequal 

 number has been noted in many other animals of several classes. The recent observations 

 of KoUiker and some other authors having elucidated the true nature of that abnormal 

 animal form, not unlike to separated arms of Cephalopods, found in the shell of the 

 (always female) Argonauta, and formerly described as a genus of worm under the name 

 of Hectocotyle by Cuvier, would lead us to expect similar males of the Nautilus living 

 like parasites with the female in her shell. There exists however not the least indica- 

 tion in the different memoirs of Owen, Valenciennes and Vrolik, that such parasites 

 were present. I can say that in Nautilus the sexual difference is not so great, and that 

 the male lives in a shell like the female. I was fortunate enough to observe one speci- 

 men of a male, which was kindly presented to me by my colleague at the Faculty of 

 Sciences of the Leyden University, the Professor of Botany, W. H. de Vriese. The 

 differences it showed in the conformation of the head may be ascribed either to sexual 

 difference or to monstrosity. This must remain unsettled till another male can be ob- 

 served ; but I incline to the first opinion, a similar aberration of structure not having 

 been observed in any of the hitherto dissected females. 



I have already described this male in a former paper', but I believe it will not be 

 superfluous to give here the translation of the chief matter of my Dutch memoir on this 

 specimen, together with some additional remarks and corrections. 



At the inner surface of the circle of digitations, which were eighteen at each side, 

 without the huod, there was a prolongation of the integuments rising up to another 

 more internal circle. This prolongation unites at the ventral side by a free and thin 

 margin to the connecting basal part of the digitations. At the inner surface of this 

 connexion of the external digitations, there are many transverse dimples parallel to the 

 transverse margin of this commissure : many little holes give a reticulated appearance 

 to this part. The prolongation becomes thicker and expands on each side in a pro- 

 cessus divided in eight digitations of different size, including each a tentacle, similar to 

 those contained in the external digitations of the head, but smaller, as usual in other 

 specimens. On account of their place, those processes seemed first to me to be analo- 

 gous to the superior labial processes of Professor Owen's memoir, because they are situa- 

 ted at the dorsal side, and consequently I described them under that name in my former 



' Tijdschrift voor de natuurkundige Wetenschappen, uitgegev. door de eerste Kl. v. h. Koninkl.-Nederl. Id- 

 stit. i. ISiS, p. 67-75. A short abstract of this description was communicated by me at the Oxford Meeting 

 (1847) of the British Association, and is inserted in the Report of the Seventeenth Meeting of the British 

 Association; London, 1848 ; Transactions of the Sections, p. 77. 



