the fresh eye, aided by the use of a hand-lens; but I may state that I did not
manage to inject any specimens, being glad to preserve the eye by at once placing,
them in glycerine and alcohol.
The iris and its ciliary processes are conspicuous objects in the sectional views,
inasmuch as the deposit of colouring matter renders them so.
With respect to the chambers and humours, PI. XXXVI, fig. 9, shows theit
relations, &c., tolerably clearly. The anterior chamber is about 0'08 inch in height,
and less than half that in opposite diameter at its widest part, namely, in the middle.
I t has a crescentic shape, though, as represented in the figure, its walls are disturbed
in position. The aqueous humour is thin, watery and clear, and the vitreous humour
is of rather a jelly-like consistence with a faint bluish tint. The contour of the
vitreous humour and chamber is decidedly pyriform.
A transverse section of the trunk of the optic nerve showed the nervous matter
along with its fibrous sheath to be no thicker than the stem of an ordinarily sized
pin; indeed, the latter had the advantage in diameter. The neurilemma in part,
and also the surrounding thick fibrous envelope, have pigment corpuscles scattered
through their tissue.
Erom the foregoing facts, which may be again briefly reiterated, viz., the rudimentary
nature of the eye—rudimentary in the absence of a crystalline lens; the
feeble development of the pigment of the choroid; the reduction of the motor
muscles of the eye to a thin muscular sheath investing a mass of blubber; the deep
imbedding of the visual portion of the eye; the glandular and tactile character of
the conjunctival investment of the cornea; and the very feeble optic nerve; all lead
to the conclusion that this mammalian eye can be of little more use than as a feeble
receiver of impressions of light. Such a conclusion is not only rendered probable
by structural conditions, but also by actual experiment. The young captive
dolphin, to which I have already referred, when objects were rapidly passed in front
of its eye, did not exhibit any manifestations of having perceived them; there was
no startling, no marked turning aside to avoid them. Moreover, the animal did
not appear to be able to ascertain the dimensions of the vessel in which it was
confined, because it invariably struck its snout against the boundaries of the tank
before it turned to describe the circuit of its limits; whilst, in contrast to this, the
fish put in beside it for its food at once knew their bearings exactly. It, however,
remains yet to be proved what are the powers, if any, of this eye under its natural
conditions of a murky liquid surrounding. Doubtless, the cornea being obscured,
so to speak, by the glandular structures which occur over it, must materially
impede the entrance of the little light that reaches it through the minute external
orifice.
But, again, there is the very remarkable feature of the tactile nature of the
investing membrane of the eye; if this be fully verified, we should have an eye quite
unique in its transitional character, and even more rudimentary than the eye of
those burrowing rodents in which the organ is invested with a thin layer of skin.
AtiA, besides, there would be the great peculiarity that this is an eye disappearing
under an aquatic life. According to our present knowledge, the only explanation to
offer for the diminutive and modified character of this eye is on the theory of disuse
arising from the absence of conditions favourable to vision; and to this may probably
be added the action, to a limited degree, of natural selection.
There are difficulties, however, even in such an explanation, because there is not
such a wide difference between the conditions of the Gangetic Platanist and those of
the Irawady dolphin, or in anything connected with their respective river-systems as
to easily account for the great degradation of the organ of vision in the one case, and
the quite ordinarily sized eye in the other, as well developed as that of any marine
Cetacean.
Urinary organs.—The kidney is a flattened, cake-like gland; in the adult 4
inches long by 350 inches in extreme breadth. The anterior end is rather pointed and
turned towards the internal border. The posterior surface is made up of forty-seven,
more or less, hexagonal lobules, flat, or slightly convex externally and packed closely
together by their opposed faces. Laterally and internally, a few of the lobules become
fused together. Nineteen of the marginal lobules of the dorsal surface are common
to the two faces of the organ, while there are twenty-nine to thirty besides these
visible on the anterior aspect, so that the kidney is made up of about eight lobules,
visible externally. They vary from half an inch to one inch in superficial area, but
are destitute of conical apices.
The cortical layer occupies the greater part of the lobules; some of the papillae
have as many as two p r three mammilliform processes.
There are generally three calyces opening into a common dilatation (pelvis of
lobule) of the duct at the base of the united lobules. In these cases generally one
of the papillae has its apex directed towards the periphery of the kidney.
Ureter.—The pelvis of the ureter is formed by the junction of six branches
resulting from the union of the secondary and tertiary ducts of the renal lobules.
The ureter altogether is 6 inches long. In the male, after leaving the kidney, it
crosses behind the lower external comer of the testicle and beyond that point it
passes behind a considerable portion of the abdominal venous plexus, which rests
on it, and immediately below this it is posterior to the transverse coil of the vas
deferens, and then a little further backwards and inwards it crosses over the descending
coil of the generative duct to the bladder. I t preserves the same general direction
in the female, running downwards to the anterior wall of the vagina till on a
level with the first great transverse fold of that channel. In the first part of its
course it lies close behind the origin of the ovary.
The renal artery and vein enter the kidney at the upper extremity of the longitudinal
groove. The artery is internal and dorsal to the vein. I t is first placed in
a deep sulcus, and the main trunk runs along the internal margin of the groove by
the side of the branches of the ureter, and divides into numerous twigs, which reach
the substance of the kidney by passing behind the ureter. The vein leaves the
kidney external and anterior to the artery and lies along the outer margin of the
groove.