Miscellaneous. 49] 
sometimes elliptical, no matter which of the two species we are 
examining. 
If we then notice, as I have been able to do, what is the sex of 
the animal, we observe that all the individuals having the mouths 
of their shells broad and more or less rounded are males, and that 
those occupying the shells with ovoido-conical, that is to say laterally 
compressed, orifices are females. 
It is true that between these two forms of orifice a few interme- 
diate ones occur, but they generally approach the rounded shape 
and belong to young male individuals, or, at least, to those in which 
the copulatory organ is not very greatly developed. These differ- 
ences in the shape of the orifice are due to the larger or smaller size 
of the spadix, which, situated on the right side of the buceal bulb, 
eventually equals the latter in bulk and requires a somewhat con- 
siderable space to contain it, while it even thrusts the bulb a little 
to the left. . The presence of these two organs, placed side by side, 
thus gives to this portion of the body a breadth almost as great as 
that of the region situate on the level of the eyes. 
In the female nothing of the kind takes place; the tips of all the 
tentacles can converge towards the same point without any diffi- 
culty, and this gives to the whole an elongate conical shape. 
The last whorl of the Nautilus shell is ‘consequently found to be 
more swollen in the males, while in the females it is more elliptical 
and has a slight tendency to be carinate ; we may further add that 
the rim of the shell is a little more undulating in the females than 
in the males. 
The appearance of the hood likewise varies according to the sex ; it 
is necessary, however, to make allowance for the effects produced upon 
the tissues by the preservative fluids, and especially by the state of 
extension in which the animal was at the moment of being plunged 
into these fluids. If the animal was strongly retracted when it was 
placed in alcohol, its hood, instead of having a regular shape, is 
more or less twisted upon itself, in which case it is a matter of some 
difficulty to detect the sexual differences that may be exhibited by 
this portion of the body. 
In the male the hood is broader, and, as Van der Hoeven very 
justly remarks, its breadth exceeds that of the female hood of equal 
length by nearly two centimetres; it follows from this condition 
that the lateral margins of the hood almost entirely conceal the eyes 
and the tentacles in the males, while in the opposite sex, since the 
hood is less extended transversely, the eyes, as well as the first pair, 
or sometimes the first two pairs, of tentacles, are quite uncovered. 
It may also be mentioned that in the females the margins of the 
hood are more sinuous and more incurvate at the level of the eyes. | 
As regards the mantle, which in the male, according to Van der 
Hoeven, is shorter and leaves the eyes almost uncovered, while 
according to the same author it extends higher up in the female, 
this organ did not exhibit these differences in the individuals that 1 
