612 EMBRYOLOGY OF THE TURTLE. Part III. 
centre. In a profile view they appear elongated, with the longer diameter trend- 
ing in the direction of the thickness of the wall. At the time the animal is 
hatched, the epithelium, (fig. 10,) at the base of the tongue, is a layer of rather 
irregular, polygonal cells, containing a moderate sized mesoblast, and a minute, 
granule-like entoblast. These cells vary considerably in size, and so does the 
mesoblast. In a transverse section of a fold of the oesophagus, (fig. 11,) we have, 
first, on the surface, a layer of epithelial cells (a) that are broader than deep, 
and each one of which is crowned with a row of vibratile cilia (fig. 12) arranged 
along the line of contact with the neighboring cells, so that their free surface is 
naked. Next beneath these is a thick layer of long, irregular, columnar cells, 
(fig. 11, 2,) the longer diameter of each occupying the whole thickness of the 
layer; and, outside of these, irregularly rounded, homogeneous, transparent cells, 
(c,) which fill up the space in the angle of a fold, and also form a thin layer 
between the columnar cells (4) and the muscular coat (d). The cells of the 
muscular coat (fig. 13) of the oesophagus are excessively long, slender, and spindle- 
shaped, and lie so closely pressed together that their long, slender ends cannot 
be well seen, unless they are separated (fig. 13a). With a magnifying power 
of eleven hundred diameters, the cell wall appears only as a rather thick, dark 
line. The mesoblast occupies nearly or altogether the whole breadth of the 
cell; it has a quite thick wall, (a,) and contains a sharply defined, single ento- 
blast (4). 
The mucous membrane of the stomach is made up of at least four lay- 
ers of cells, (fig. 17, a,) piled one above the other, so as to resemble columnar 
cells. Those next the inner surface of the stomach are the largest; and, pro- 
ceeding thence outwardly, they grow smaller. The mucous membrane of the thick 
intestine is composed of no less than six layers of cells (Pl. 21, fig. 18, a-«’). 
In those cells which are next to the surface, (a’,) the mesoblast is very easily seen ; 
but in the other more exterior cells it is very faint. By separating a few col- 
umns of cells, (fig. 18a, 18b,) not only may their relations be better shown, 
but the clear, round mesoblast, and its sharply defined entoblast also become vis- 
ible. These cells are placed so regularly one above the other, that they resem- 
ble a long columnar cell. When seen in a mass, through considerable depth, 
they appear oval, with the longer diameter of each trending im the same direc- 
tion as the columns (fig. 18); but, taken singly at a fixed focus, their more or 
less polygonal shape (fig. 18a) may be recognized. Those at the surface (fig. 
18, a’) are the largest, and those at the outermost side, (a,) nearest the muscu- 
lar layers, (¢, d,) are a great deal smaller; and between these two extremes there 
is a regular gradation. Here and there a few cells were found in a state of self 
division (fig. 18, a, b); some (a) had two distinct mesoblasts and a strong median 




