Cuap. II. HISTOLOGY. 601 
2, w-c. 1, n°, p. 553,) from its lower side; the remainder constituting the true intes- 
tine, called the thick intestine, in this region of the body. Not much later, the 
anterior blind sac becomes changed, by the folding together of the two opposite 
halves of its superior arch, to form a pendent double curtain, or support of the 
intestine, the mesenterium, and, by the separation of a portion of its lower side, 
to form the windpipe (Pl. 24, fig. 1, I”, 2”) and the lungs (J, 2). The greater 
portion, (I, 1’, 2’, 2”,) however, remains, and develops into a double-walled chan- 
nel, the oesophagus (I, 2”) and the stomach (J’, 2’). The inner wall (2’, 2”, and 
fig. la, 2 2”) constitutes the epithelial layer, otherwise called the mucous mem- 
brane, and is continuous with the inner wall (fig. 1, 2, 2”, fig. la, 2, 2”) of 
the lungs and windpipe. Exterior to the embryo, the continuation of the outer 
wall (fig 1, I, I’) of the intestino-subsidiary layer is very thin, and the inner 
wall (fig. 1, 2’, 2”) loses its compactness, and becomes continuous with a rather 
thick layer of large hyaline cells, (see Pl. 17, fig. 5, and p. 566,) which under- 
lie the vascular area. The double pendent curtain, or mesenterium, soon forms 
along the abdominal region, still retainmg its thick, double walls (Pl. 9e, fig. 8, 
n®, fig. 8a, n®) after. the intestine (fig. 8, m7; Pl. 18a, fig. 7a, mn’, fig. 8, n', n’, 
n’, fig. 9, n', nv’, nv?) has become so long as to protrude through the abdominal 
opening. 
The Glands of the Stomach. (See p. 571, and Pl. 21, fig. 14-16, etc.) 
The Lungs. (See p. 555, and 556, and Pl. 24, fig. I, la,. ete.) 
The Lwer. (See p. 505 and 556, and Pl. 24, fig. 9, 7, fig. 9a, 7, etc.) 
The Gall Bladder. (See p. 563, and Pl. 18a, fig. 5, u, etc.) 
The Wolffian Bodies. (See p. 552, and 560, and Pl. 18a, fig. 8, ete.) 
The Kidneys. (See p. 566, and Pl. 25, fig. 4, 6, and w-ce. 2, 3, etc.) 
The Ovaries and Spermaries. (See p. 567, and w-e. 2, 7, ete.) 
The Urinary Bladder. (See’p. 572, and Pl. 25, fig. 1, n°, etc.) 
The Allanios, (See p. 553, and Pl. 13, fig. 2, w-c. 1, n°, ete.) 
S HG TH Oe 1Xs. 
HISTOLOGY. 
In a former section’ we have demonstrated beyond question, that the embry- 
onic disc, at the time of its formation, and the peripheric portion of the 
germinal layer, are composed of a uniform layer of consimilar cells (Pl. 9a, fig. 
1 See Part III., Chap. 1, Sect. 5, p. 479. 
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