Cuap. II. HISTOLOGY. 617 
p- 570,) there is a mixture of oval, flat, disc-formed corpuscles (PI. 19, fig. 12, a, 4) 
with those which are oval and partially flattened, (fig. 9, 10, a, 4, ¢, ¢’,) whilst 
others, although oval, are not flattened in the least (fig. 11, a, 4, ¢ d, e), 
These last (fig. 11) are evidently derived from the elongation of the globular 
corpuscles of earlier stages (fig. 7); for, except in shape and a little difference 
in size, the two kinds differ but very little. An end view (fig. 11, ¢, d) 
of the oval corpuscles is not distinguishable from that of globular forms, (fig. 
7,) except that in the oval ones the mesoblast is not lateral, but central. In 
order to become disciform, as in the adult, the corpuscles gradually flatten, (fig. 
9, 10, a, 6, e, ¢,) until the two opposite sides almost touch each other (fig. 12, 
a, 6, fig. 13, 13a, 13b, 13c). At this period, they have a remarkably plastic 
nature, and, when in contact, mutually flatten against each other, (fig. 13, 13a,) 
or stretch out to a considerable extent, (fig. 15b,) if they catch against any 
thing whilst floating on the stage of the microscope. The mesoblast is very 
faint and perfectly homogeneous in the most advanced phase, a short time before 
the birth of the Turtle. Finally, in the adult, the blood corpuscles (fig. 8, @ 
to 7) are quite flat (c); but the centre is not depressed, as would appear from 
a side view (a, 6). The clear, homogeneous, light mesoblast contains a much 
darker entoblast. In water, the walls of the parent cell, the ectoblast, (7) col- 
lapse, and the mesoblast and entoblast blend mto one darker mass. By drying, 
the thickness of the parent cell (4) becomes sharply defined, and very conspic- 
uous. 
The Muscles. A short time before the Turtle is hatched, the muscles differ in 
the degree of development to which they have arrived in various parts of the 
body. At the point where the dorsal muscles are attached to the arch of the 
vertebre, they consist of a mass of spindle-shaped cells, attached obliquely to each 
other, (Pl. 19, fig. 23, 6,) or ‘of very long, slender cells (a). The former () 
resemble the cells of the dorsal arch, (c,) and have a large, oval mesoblast, which 
contains numerous granules; the latter have lost their mesoblast, and have become 
so intimately united to each other as to obliterate the intervening walls, and thus 
assume the appearance of long, slender cells. Some of the mesoblasted cells 
are thus united to those without mesoblasts. The granular contents of these 
united cells have a more or less linear arrangement. Presently we shall see 
what this peculiarity tends to. In the foreleg, the muscular fibres have all the 
characteristic appearances of the adult. The longitudinal and the transverse strix 
25, a). The fibrille (fig. 25, 4) which 
of the fibres are readily seen (PI. 19, fig. 
gs of very minute granules, such as we 
constitute the fibres (#) are mere strin 
saw in another part (fig. 23, a, b) of the body, near the dorsal arch. Here, 
however, they are more regularly arranged in lines, but have not lost their gran- 
78 
