152 DR. COBBOLD ON THE EYE OF THE COD-FISH. 
III. The normal condition of the retinal cones in the Cod is 
double, and the phenomena exhibited by these twin-cones, under 
the action of water, seem to indicate that the bacillar prolon- 
gations (Zapfenstibchen) of the cones are not persistently formed 
appendages, as the representations of Koélliker, H. Miller, and 
Nunneley would lead us to suppose, but bear more the character | 
of tactile bodies capable of protruding filaments under the influ- 
ence of stimuli. 
The cones and bacilli of Jacob’s membrane are not true nerve- 
structures in the sense maintained by Kélliker and Miller, neither 
can they properly be called “ percipients of light; but they are, 
in point of fact, special tactile organs, like the Pacinian corpuscles 
of the skin, and are destined to receive and convey impressions 
produced by pencils of light impinging upon and reflected from 
the internal limiting membrane of the choroid,—the impressions 
being subsequently and finally transferred to the true nervous 
elements of the inner layer of the retina by the intervention of 
the granular layers, which are held together by the delicate Miil- 
lerian filaments. 
Although I have arrived at the above conclusion respecting the 
Pacinian-corpuscular character of the cones from independent and 
oft-repeated examinations, I may observe that a similar opinion 
had been previously recorded by Professor Goodsir of Edinburgh, 
who, from considerations affecting the development of the verte- 
brate eyeball, goes even further, and asserts that the bacillar 
layer, with its rods and cones, “belongs morphologically to the 
transparent humours of the eye.” 
All observations made on the retina after it has been immersed 
in solutions of chromic acid, in so far as the intimate histological 
characters are concerned, should be received with extreme caution, 
because the normal characters of its component parts are at once 
destroyed by the addition of coagulating reagents. The same 
remark is equally applicable to the vitreous body and other soft 
tissues of the eyeball. Strong acid solutions, however, are useful 
in determining the relations of the ultimate elements of any given 
compound tissue, as has been abundantly proved by recent inves- 
tigations, and more particularly by those of Hannover, Kolliker, 
and Heinrich Miiller. 
