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attached to the free surface, imbedded in an intermediate substance 
or matrix, which is of a homogeneous nature, or contains more or 
less dark granular matter. These rods are prolongations of the 
cylinders contained within the tubes of the follicular coat. In the 
deeper portions of the tissue, the matrix is softer, and the granules 
more numerous, darker, and more distinct, often resembling cell- 
nuclei. The whole structure becomes less defined, and more blended 
together as it approaches the free-surface. 
The further arrangement of this tissue varies in different birds, 
the variations being dependent upon those in the follicular layer. 
The cylinders are sometimes irregularly scattered, sometimes disposed 
in lines or linear groups, and in other cases collected into small 
triangular or polygonal groups. In the latter, the dark granules of 
the matrix are arranged in distinct intersecting lines, partitioning off 
the more transparent spaces, which contain the bundle of rods, and 
so definitely disposed as to give a beautifully reticulated appearance 
to a fine horizontal section. 
The follicles bear so much resemblance in their appearance and 
situation to the gastric glands of other animals, that for some time 
I believed that their object must be the secretion of a fluid to assist 
in digestion, and that the cylinders of the epithelial coat were the 
ducts which conveyed this secretion to the free surface ; but having 
failed in repeated attempts, by every method with which I am ac- 
quainted, to demonstrate their tubularity, I am obliged to revert to 
the idea that the office of the gizzard in the digestive process is 
purely mechanical. The function of these numerous follicles appears 
to be nothing more than the secretion of the horny membrane which 
lies over them, a rod being formed in the bottom of each, and gra- 
dually pushed up, very much in the manner in which a hair is de- 
veloped; while either the upper part of the tube or the interme- 
diate surface pours out the substance which fills up the space between 
the rods, and consolidates the whole tissue. As in ordinary epithe- 
lial tissues, this process must be constantly going on ; as new forma- 
tion takes place below, the'surface is worn off by continual friction 
with the hard substances taken into the cavity of the gizzard. 
I will next describe the peculiarities of these structures in a few 
particular examples :— 
Thrush, Blackbird, Nightingale (Turdus, Sylvia). —In_ these 
birds the epithelial lining of the gizzard is comparatively thin, and 
not very hard; but yet it presents the characteristic structure de- 
scribed above. A transverse section shows the cylinders arranged 
more or less regularly in lines, but the intermediate substance is uni- 
formly granular, and does not present distinct dark lines partitioning 
off groups of rods, as in the following birds. 
Sparrow, Bullfinch, Yellowhammer (Passer, Pyrrhula, Emberiza). 
—Here the cylinders are more distinctly arranged in groups, each 
consisting of a long single row, generally of as many as six or eight. 
Fowl, Guinea-fowl, Quail (Gallus, Numida, Coturnix).—In the 
true gallinaceous birds the follicles are collected into very definite 
oval or polygonal groups. The epithelial layer is thick and horny, 
