Cuap. II. HISTOLOGY. 613 
constriction, made more conspicuous by the total absence of granules at that point, 
and others (4) had but a single, clear, distinct mesoblast, probably the old one, 
near one end, and at the other, on the opposite side of the constriction, a very 
faint one, without doubt just forming. By this we may very readily account 
for the fact that there are but two layers of cells (fig. 11, a, 4) in the ceso- 
phagus ; while there are four layers (fig. 17, a) in the stomach, either four or 
five (fig. 19, a, a) in the long intestine, and six here (fig. 18, a, a). Directly 
beneath the mucous membrane is a layer of rounded, loosely packed cells, (4,) 
identical, to all appearance, with those seen in the same relation in the ceso- 
phagus (fig. 11, c). Next, and farther outward, is the layer of constrictor mus- 
cles, (c,) composed of elongated, fusiform cells, similar to those of the same layer 
in the cesophagus, (fig. 11, ¢,) which trend in a direction transverse to the axis 
of the intestine. Just exterior to this is another layer of muscle, (d,) which is 
composed of similar cells, but they trend at right angles to the last, and_there- 
fore along the intestine. In a transverse section of the intestine, these cells are 
eut across, so that their shorter diameters are exposed. A thin, apparently amor- 
phous membrane (¢) incloses the whole intestine. The mucous membrane (fig. 
19, a) of the long intestine, at a point about one third of its length behind the 
stomach, hardly differs from that of the thick intestine, (fig. 18, a, a’,) except that 
the layers of cells are only four or five in number, and the cells a little smaller. 
The rounded, loosely packed cells (4) just outside of the mucous membrane (a) are 
also a little smaller than in the thick intestine; but the muscular layers (¢, and 
d) and the enveloping membrane (e) do not appear to differ. The glands of 
the stomach are very much elongated, and more or less convoluted (fig. 17, 4, 
ec, d). Their walls are composed of cells, which are identical in every respect 
with those of the mucous membrane, (a,) of which they are a direct continuation. 
When the gland is perfectly straight, the cells (¢) on its inner surface are as large 
as those (a) on the surface of the stomach; but where the gland bends, those in 
a similar position at the inner angle of the bend (d) are compressed, whilst those 
at the outer convex surface of the curve are the largest. The cavity (4) of the 
glands is very narrow, from its opening to its bottom. 
The Allantois. A short time before the young are hatched, the allantois is 
composed of two layers. At a point near the body of the embryo, the inner 
one (Pl. 9a, fig. 50) of the two is made up of rather large, thick-walled, irreg- 
ularly polygonal cells, filled by minutely granular but transparent contents. The 
outer layer (fig. 30a) is distinguishable only on account of its numerous dark 
granules, which are arranged in heaps; the cells which, in all probability, sur- 
rounded them, could not be discovered. At a point more distant from the embryo, 
A 
the cells of the imner layer (Pl. 18a, fig. 3) are larger and more elongated, and 
