608 EMBRYOLOGY OF THE TURTLE. Part III. 
terminal bones (PI. 21, fig. 21) of the feet have not yet assumed the cartilaginous 
state, but are composed of sharply polygonal cells (fig. 2la) in contact with each 
other. Each cell contains a large mesoblast occupying half its diameter, and 
numerous entoblasts. Just before hatching, the centre of the bones of the limbs 
contains pure cartilage cells (Pl. 22, fig. 5, 6, 6a, 6b). The intercellular substance, 
or blastema, (a,) so called, occupies a large amount of space, when contrasted with 
the size of the cells (4). These cells are very irregular in shape, varying from 
spherical, semiglobular, trianguloid to elongate-oval, and each one contains a large, 
faint mesoblast. The principal pomt of interest is the granular basis for lime 
deposits in the form of a central heap, with branches stretching out in various 
directions. Some of the cells (fig. 6) also contain faint granules throughout their 
whole length and breadth. The application of alcohol brings out more clearly 
the faint granules, (fig. 6a,) and also those arranged in a branching manner. In 
some instances, the cells thus treated shrank away from the surface of the cavity 
of the blastema (fig. 6a, ¢, 6b). 
The Skin. At the time the branchial fissures begin to form, and the eye to 
develop, (Pl. 12, fig. 5, 8, 9, 9a, 11,) the surface of the tail consists of hyaline, 
oval cells, (Pl. 19, fig. 2,) each one of which contains a small, sharply defined, 
single mesoblast. A little later, the cells on the head, near the eye, are large, 
cylindrical, thin walled, and hyaline, and appear to have no contents whatever 
that may be seen, not even a mesoblast. They form but a single stratum, and 
have scattered between them minute hyaline granules. Considerably later than 
this, (Pl. 14, fig. 2, 2a,) the cells of the dermal layer (Pl. 19, fig. 4, f) are 
globular, hyaline, and contain each a single, dark mesoblast (see fig. 7, 2)... When 
water is applied to these cells, the mesoblast becomes resolved into two bodies, — 
one very transparent, and the other dark and granular (fig. 4, a). When the 
toes begin to develop, (Pl. 25, fig. 11,) the cells of the surface of the feet are 
globular, faintly granulated, and contain a large, single, clear mesoblast, and a 
single entoblast (Pl. 21, fig. 25). The internal tissue of the feet is composed 
of cells similar to those of the shield (fig. 26). At this time, the cells of the 
skin of the carapace are elongated, irregular, finely granulated, and each contains 
a large mesoblast and a central, single entoblast (Pl. 21, fig. 26). That portion 
of the skin which is metamorphosed into claws (Pl. 21, fig. 20, @) is composed 
of very large, transparent, irregularly polygonal cells, each one of which contains 
a minute, irregular mesoblast, situated at its surface, and a dot-like entoblast (fig. 
20a, 20b, 20c). The cells (fig. 20, 6) beneath this horny sheath and at the 
base of the toe (0) are large, (fig. 20d,) but yet much smaller than those of 
? Although this is a blood corpusele, it is apparently identical with the cells of the dermal layer. 


