614 EMBRYOLOGY OF THE TURTLE. Part III. 
lozenge-shaped, and have thicker walls. The outer, granular layer is very distinct, 
and contains the bloodvessels. 
The Urinary Bladder. At the time of hatching, the mucous membrane of the 
bladder is composed of five layers of cells, (Pl. 20, fig. 15, 13a,) very similar to 
those of the long intestine, (Pl. 21, fig. 18, 18a, 18b,) the only difference being that 
there is one layer less, and that the cells of the several layers are more strictly 
on a level with each other (Pl. 20, fig. 13a). When seen from the inside of 
the bladder, the superficial cells (fig. 15) appear more or less polygonal, but yet 
their walls are slightly rounded. The mesoblast of some of them is elongated, 
and contains two entoblasts, an arrangement which is often indicative of a ten- 
dency to a selfdivision of the cell. In an expanded state of the bladder, the 
cells lose in a measure their polygonal shape (fig. 15). The muscular coating 
(fig. 16) is a mesh-work of superposed fibres, which run in every possible horizontal 
direction. These fibres are composed of elongated, fusiform cells, (fig. 14, I4a,) of 
variable length, according to their position. The outermost fibre cells are lozenge- 
shaped, about twice as long as broad, and excessively transparent. The large, 
round mesoblast is not so faint as the cell, and the entoblast, sometimes double, 
is sharply defined. The rest of the whole muscular system is composed of elon- 
gated, spindle-shaped cells, (fig. 14,) with faint, granular contents and a large mes- 
oblast occupying nearly the whole width of the cells, which have none of the 
long, thin, tail-like prolongations seen in the oesophagus (Pl. 21, fig. 15, 13a). 
The Lungs. At the time the lungs have fairly separated from the intestine, 
(Pl. 24, fig. 2, ¢ ¢, and fig. 2a,) the imner wall, or mucous membrane, (PI. 20, 
fiz. 12, 4,) is composed of a single layer of broad, cylindrical cells, with rounded 
outer ends. A short time before birth, the mucous membrane is composed of 
a single layer of cells, (Pl. 20, fig. 7, 9, a, 11, a,) of variable size, in different 
portions of the lung. ‘They contain very scattered, granular contents, and vary 
in shape; some being broader than deep, (fig. 9, a, 11, a,) and others (fig. 7) 
much deeper than broad. The contractile tissue (fig. 10, 4, 11, 4) is a deli- 
cate, fibrous mesh, forming, with the mucous membrane, (fig. 11, a) the walls of 
the cavities. The bloodvessels (fig. 10, ¢) do not follow the trend of the fibres 
of the mesh, but run at various angles across them, and in close proximity to 
the mucous membrane (fig. 7). The outer surface of the lung is covered by a 
thin layer of very pale, round cells, (fig. 9a, 11,) which do not touch each 
other, but are separated by numerous dark granules. Besides these, the surface 
is mottled, principally over the course of the bloodvessels, (fig. 5,) by numerous 
pigment cells, (fig. 8, 9a, 11,) which are nothing more than the pale cells, around 
which much darker granules are densely packed, in such a manner as to assume 
the appearance of an irregular two, three, four, or five-rayed star. 



