It will be found from an examination of the foregoing descriptions that
in those specimens in which the sex is known to be female, or is marked
as such, the premaxillæ are comparatively narrow, the mesirostral
ossification only slightly developed, the prenarial basin undeveloped,
and the teeth quite slender, with a diameter of from 10 to 14 mm. As the
teeth in some of them have closed roots there can be no doubt that they
are adults. On the other hand, those skulls known or believed to be from
adult males have the mesirostral ossification enormously developed, a
deep prenarial basin, and fusiform teeth with closed roots and a diameter
of from 25 to 30 mm. It appears to be a fact, therefore, that in the
females the mesirostral ossification is never greatly developed at any
age, that the teeth are never thick and fusiform, and that the prenarial
region is never deeply concave. Immature individuals present, of course,
the appearance of the females, except that the teeth are open at the root
and that the mesirostral ossification is not developed at all.
Conversely, the females, broadly speaking, always present characters of
immaturity, but in adults the roots of the teeth are, of course, closed.
That these conclusions are correct is borne out by an examination of
descriptions and figures of specimens from other parts of the world, for
which purpose a few are available in the writings of New Zealand
zoologists and others. Hector, for example, in 1873,[40] published a
description and figures of a skull from the Chatham Islands which had a
large mesirostral ossification, deep prenarial concavity, and large,
thick teeth, having a diameter of 34 mm. This is the same combination of
characters found in the Newport specimen, which is known to be a male,
and the Bering Island skulls supposed to be those of males.[41]
In 1876,[42] Haast figured and described a female 26 feet long, and hence
presumably adult, from Lyttleton Harbor, New Zealand, which had a small
development only of the mesirostral ossification, a slight prenarial
depression, and rather slender teeth with closed roots and a diameter of
19 mm. This combination of characters is found in the Barnegat skull,
also known to be an adult female.
In the same paper Haast describes[43] and figures the skull of another
female from Akaroa Harbor, New Zealand. This individual was larger than
the last and was accompanied by a suckling calf. Hence, there can be no
doubt that it was mature. The skull shows a moderate development of the
mesirostral ossification, and slender cylindrical teeth with closed roots
and a diameter of 16 mm.
It is demonstrated from the foregoing discussion, I think, that the sexes
can be distinguished by the skulls, when adult, or by the teeth alone.
Reverting now to _Ziphius gervaisii_, which was mentioned on p. 30 as
perhaps constituting a separate species, it will be seen by examining the
figures given by Gervais[44] of the skull on which it was based that the
latter presents the combination of characters peculiar to the female of
_Z. cavirostris_. This skull, which was from Aresquiers (Hérault),
France, was 888 mm. long, and hence, presumably, adult. The mesirostral
ossification is but slightly developed, the prenarial concavity moderate,
the teeth small, slender, and cylindrical, with closed roots and a
diameter of 14 mm. There seems to be no sufficient reason for regarding
this skull as representing a species distinct from _cavirostris_.
The specimen from Buenos Ayres described and figured by Burmeister in
1868[45] was an immature male. In the skull the mesirostral ossification
was lacking, the premaxillæ were flat, and the teeth conical and
acuminate, with open roots, and a diameter of 12 mm. This individual was
12 feet 11½ inches (3.95 m.) long, and hence about as long as the
Charleston specimen, but the skull was apparently 680 mm. long, while
that of the Charleston specimen is 797 mm. long. In the latter the teeth
are 45 mm. long and 10 mm. in diameter, while the tooth figured by
Burmeister is 31 mm. long and 12 mm. in diameter. From these data it
appears improbable that the sex of immature individuals can be determined
from the skull or teeth.