Cuap. II. FOLDINGS OF THE EMBRYONIC DISC. 571 
32c). These bands traverse the whole thickness of the lens, and converge toward 
its two opposite sides (Pl. 21, fig. 31, 82, a). 
The shape of the blood corpuscles varies; some are quite flat, (Pl. 19, fig. 12, 
a, b,) and others are more or less thick, (fig. 10, a, 6, ¢, ¢,) and even perfectly 
round when seen endwise (fig. 11, ¢, d). The liver is strongly bilobed and very 
much flattened (Pl. 25, fig. 1, 7, 7); and at one point (fig. la, 7) it clings very 
closely to the stomach (fig. la, x”). The cells (Pl. 19, fig. 32, a, b, 0, ¢, ¢) of 
the liver are as characteristic as in the adult, with their large mesoblast, coarse, 
granular contents, and strongly polygonal shape (fig. 32). 
The partitions of the lungs are very numerous, (PI. 20, fig. 5,) and have a 
distinct fibro-muscular structure (fig. 10, 4, fig. 11, 4); the cells of the epithelial 
layer (fig. 9, a, fig. 11, a) are broad and deep. The surface of the lungs is coy- 
ered with a layer of very faint, round cells, (fig. 9a and 11,) with minute granules 
interspersed between them; and, along the courses of the bloodvessels, there are 
numerous black pigment cells (fig. 5, 8, and 11, J’). The cartilaginous rings of 
the trachea (Pl. 24, fig. 6) form a nearly continuous spiral; the cartilage cells of 
this organ are sharply polygonal, and as yet pretty close together (Pl. 20, fig. 6). 
The “intestine (Pl. 25, fig. 1, n', w, fig. la, u', n?, n*) is very long and much 
convoluted ; its anterior opening is furnished with a well developed hyoid bone 
(fig. la, oh); the neck (fig. 1, 7) of the yolk sac, where the intestine connects 
with it, is very small and scarcely perforated. The folds of the imternal surface 
of the cesophagus (Pl. 25, fig. 1b) are broad, and have narrow but deep inter- 
vals; but at its posterior part the folds widen considerably as they pass into 
those of the stomach, where the intervals are very narrow and shallow. Just 
behind the stomach the folds are very narrow and wavy, and the intervals are 
broad, but rather deep (fig. 1c). In the thick imtestine, close to the cloaca, the inter- 
nal folds (fig. 1d) are almost as narrow as those in the small intestine just behind 
the stomach, but perfectly straight; and the intervals are very broad. Through- 
out the whole length of the intestine there is a well-developed, thick epithelial 
layer of polygonal cells, (Pl. 21, fig. 1, 3, 4, 5, a, 6, 14a, 14b, 14c, 14d, l4e, 
14f, 14g, 54,) covered with vibratile cilia, and beneath this layer a thick stratum 
of long, columnar cells, either in a single layer, (fig. 2 and 5, 4,) or, in the thick 
intestine, in two or three layers (fig. 34). The whole surface of the stomach is 
marked by little apertures, (fig. 14, a, 14a, 14b, fig. 15, 15a, 4,) leading into 
quite deep depressions or sacs, (fig. 16, 16a, 16b,) which are lined with a contin- 
uation of the epithelial layer (fig. 16b). 
The uriniferous tubes (Pl. 25, fig. 5, 6) of the kidneys are a great deal thicker 
than those (a) of the Wolffian bodies. The urimiferous tubes (Pl. 20, fig. 1, la, 1b) 
of the Wolffian bodies are composed of very large and transparent cells. The neck 
