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 
nuinber has been noted in many other animals of several classes. The recent observations 
of Kolliker 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 hvod, 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 KI. v. h. Koninkl.-Nederl. In- 
stit. i. 1848, 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. 
