Cuap. II. HISTOLOGY. 615 
The Trachea. A short time before birth, the cartilage rings of the trachea, 
(Pl. 24, fig. 6) are composed of quite thick-walled cells, which contain numerous 
minute, dark granules (Pl. 20, fig. 6). The cells are as yet in close contact 
with each other, and have sharp, polygonal contours. At birth, the cartilage 
cells (fig. 3, 2) are widely separated from each other by the development of an 
amorphous, intercellular substance. At the middle (4) of the ring, these cells are 
more or less rounded; but, as they approximate the fibrous bands (a) which 
alternate with the rings, they gradually flatten, and diminish in size, till, at the 
edge (ec) of the layer, they are mere thick, dark lines) The fibrous bands (a) 
consist of very fine threads, or strings, of granules, interwoven, and oftentimes 
crossing each other at very broad angles. 
The Liver. A short time before the Turtle is hatched, and about the period 
when the allantois has surrounded the whole yolk sac, the cells (Pl. 19, fig. 32) 
of the liver are moderate in size and polygonal. They are filled by densely 
crowded, dark granules, in the midst of which is a clear, round mesoblast. When 
separated from each other and immersed in water, they assume a spherical form 
(a, 0, U', ¢, &). Just before birth, the liver cells are much larger than those 
mentioned here. They are more or less polygonal, and contain a crowded mass 
of coarse, dark, oily looking granules and a bright yellow mesoblast, with a 
minute, sharply defined entoblast (fig. 31, a). When isolated (4) from each other, 
and treated with a little water, they show that they have (a) very thin walls 
and a rather opaque but bright yellow mesoblast. 
The Gall Cyst. At the last stage mentioned, the wall of the gall cyst is a 
single layer (Pl. 19, fig. 29) of cylindrical, wedge-shaped cells, with the broader 
ends next to the outer surface (a) of the wall. They are very transparent, and 
contam scattered, faimt granules and an excessively hyaline mesoblast near the 
broader end. Seen endwise, they appear polygonal (fig. 29a). 
The Bloodvessels. Just after birth, a bloodvessel that had been isolated from the 
pia mater had an excessively thin wall, (Pl. 19, fig. 14,) which appeared to be 
built up of excessively hyaline, polygonal cells, each one of them containing a 
large but rather faint mesoblast and perfectly homogeneous contents. In some 
places, the mesoblast appeared in profile (a, 4); yet outside of it no wall, but 
that of the cell, could be detected. 
The Gental Organs. Just before the Turtle is born, the ovary (see p. 573 
and Pl. 25, fig. 7, x) is composed of moderately large, polygonal, and extremely 
transparent cells, (Pl. 19, fig. 30,) each one of which contains a large, densely 
granulated mesoblast. 
The Kidneys. By the time the embryo can freely move its eyes, jaws, and 
toes, (see p. 565, and Pl. 18a, fig. 2 and 3,) the Malpighian bodies (Pl. 20, 
