NUNNELEY, ON THIS RETINA. 223 
are comparatively few in number, the greater part of them 
are conoidal or fusiform in shape, the base being without, 
and they are surmounted by a highly transparent coloured 
globule, which is clesely attached to and partly imbedded in 
the end of the rod. The number of the true cylindrical rods 
in aquatic birds, as the duck, goose, or swan, appears to be 
very much less than in land-birds; indeed, in some it is 
questionable if all the rods are not more or less conoidal in 
shape, but they are so to a less extent than are those of land- 
birds. The globules are evidently cells filled with a coloured 
fluid, which reflects light almost like oil, but is not oil; for 
the cells are not soluble in either spirit of wine, or dilute 
potash, ammonia, acetic or chromic acids; and when the 
globules are crushed, and the coloured fluid has run together 
and dried, it is soluble in water, while the dried globule, by 
immersion in water, swells out to even a greater than its 
normal size. They are unaffected by immersion in boiling 
water; they are well seen by the addition of chromic acid ; 
and then, if liq. potassee be added, the colour is destroyed, 
but their shape and size are well shown; the rods are dis- 
solved, and thus they are left free. Many of the globules are 
of a beautiful ruby red; others, and the greater number, 
three or four to one, of a canary yellow, some approaching to 
a green tinge ; some few I have seen of a decided green colour, 
and in some the colour is so pale, as to be hardly perceptible. 
Though the yellow are the most numerous, the ruby are for the 
most part the largest. There is no fixed relation either in 
number or size, nor are those of the same colour always of the 
same size, varying in the bird from 5,'55 to psboo of an inch; 
and I think the size, number, and relative proportion 
of the two colours differ in different parts of the same 
retina. In a guinea fowl, I found the globules very nearly 
uniform in size, about the 5-55, of an imch, and the 
globules of pretty nearly the same tints of ruby and canary 
colours. I have found there is more variation in size and 
colour of the globules in young fowls than in old. Though 
closely imbedded in the rods, they easily become detached 
and float about; they are also attached to the choroid coat, 
but not so intimately as to the retina, for in separating it 
from the retina they always adhere to the latter. They are 
much more persistent than most of the other elements of the 
retina, and may be preserved, when dry, for some time. 
Hannover, who was the first to describe these bodies, has 
fizured the ruby as attached to what he calls cones jumeaua, 
and each of these as surrounded by six rods, surmounted 
each by a yellow globule, forming a setting for the ruby. I 
