333 
and in it each little bundle of rods is distinctly circumscribed by 
septa formed of dark granules (Pl. CLXV. fig. 1). In the first named, 
this layer at its thickest part measures = inch, and the follicular 
stratum is =), inch deep. 
Duck (Anas boschas).—Although so different in its general cha- 
racters and habits, in the structure of the gizzard the duck closely 
resembles the fowl. A transverse section of either the follicular coat 
or the epithelial stratum of the two birds would be almost undistin- 
guishable from each other under the microscope. 
Pigeon (Columba livia).—The triturating disks are well-marked 
in this bird, three-quarters of an inch in diameter, but rather longer 
from above downwards than from side to side. The epithelial coat 
is well developed, being 1, inch in thickness. Its transverse section 
shows long dark lines, nearly parallel, with occasional cross lines, 
marking off the cylinders into groups, not quite so regular and elon- 
gated as in the passerine birds, but presenting a greater affinity to 
these in this respect than to the true Gallinacee. The tubes of the 
follicular membrane have a similar arrangement when seen in cross 
section (Pl. CLXVI. figs. 1 & 2). In Hetopistes migratorius and 
Goura victorie the structure is precisely similar. In the last the 
epithelial coat is very hard, and measures as much as ;}, inch in 
thickness. 
Nicobar Pigeon (Calenas nicobarica).—On each side of the in- 
terior of the gizzard (corresponding in position to the triturating 
disks in other birds) is a hard horny body, perfectly circular in out- 
line, inch in diameter, detaching itself when dry (in which state 
only I have seen it) from the remainder of the epithelial lining, 
as distinctly as if struck out by a punch. It is concave, rough, and 
yellow on the free surface, quite smooth and very convex (almost 
pyramidal, the sides sloping up to an apex in the centre) on the 
attached side, where it is imbedded in a corresponding hollow in the 
mucous membrane. When dried it is of almost stony hardness, and 
in section opaque and white. Its average thickness is } inch. The 
other parts of the gizzard are lined by a membrane presenting the 
usual characters of that found in pigeons. On examining the fol- 
licular layer microscopically, it was found to be similar in structure to 
the same tissue in other members of the family ; but in that part over 
which the disks lie, the follicles appear more evenly distributed, and 
not so distinctly collected in linear groups as in other portions of the 
organ. In the thin part of the epithelial lining of the gizzard the 
cylinders are collected into irregular groups, most of them having 
a somewhat oval or linear form in transverse section ; the interme- 
diate granular lines being dark and well-marked. On moistening the 
attached surface of the disk, it was seen to be covered with the usual 
little filamentous bodies drawn out from the follicles. Vertical sec- 
tions showed parallel rod-like bodies with little intermediate or gra- 
nular substance. Horizontal sections confirmed this view. The rods 
are either round, oval, or of somewhat polygonal form, mostly of 
nearly uniform size, and showing a darker central portion, and closely 
packed together, with little intervening substance, and not collected 
