470 CETACEA. 



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, ^g. 9, shows their 

 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. 

 It 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 pyrif orm. 



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 rudi- 

 mentary 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 oJL 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. 

 And, besides, there would be the great peculiarity that this is an eye disappearing 



