478 EMBRYOLOGY OF THE TURTLE. Part III. 
boiled. The homogeneous state of the contents of the Purkinjean vesicle usually 
appears about the time when the egg is one quarter of an inch, or a little less, 
in diameter (Pl. 9, fig. 7). The whole vesicle, as we have said above, is filled 
with homogeneous contents; but upon closer examination it may be perceived that 
the mass is composed of excessively minute particles, which the heat of boiling 
arranges in little clusters (Pl. 9, fig. 7b) that might easily be mistaken for a 
coarse granulation. This clustering is most evident at or near the centre of the 
field, where it seems to be denser and darker (PI. 9, fig. 7a). For comparison 
with this, we will cite the figures of a larger egg, (PI. 9, fig. 9,) more than 
two thirds grown, where the only difference from the last is, that the clusters 
of particles (fig. 9a, fig. 9c, a, 6) are not so large, but more densely packed at 
the centre, and the Purkinjean vesicle is more deeply indented (fig. 9b). Another 
and little older phase (Pl. 9, fig. 10) offers a new feature in the contents of the 
Purkinjean vesicle; boiling has not had the effect to coagulate imto clusters the 
minute corpuscles which form these contents (PI. 9, fig. 10c, a); and, excepting 
perhaps that the central darker and coarser granules (Pl. 9, fig. 10a, 10c, 4) 
whose brilliant refraction renders them so conspicuous are brought more closely 
together than is natural, there is nothing left but the deep indentation of the 
vesicle (fig. 10b) to indicate that a contracting influence has been at work. 
The next and last step in the life of the Purkinjean vesicle is an almost 
total vanishing of its clusters, (Pl. 9, fig. 11b, @,) so conspicuous heretofore in the 
medium sized eggs when boiled; but, as these clusters grew more and more faint 
latterly, we are not taken by surprise at their nearly total extinction in the full- 
grown egg (PI. 9, fig. 11). Still a few brilliant, darkly outlined granules, situated 
centrally, and not so coarse nor so numerous as in the last-mentioned vesicle, 
serve to cloud the contents which elsewhere are homogeneous. At this age, too, 
the wall (Pl. 9, fig. 11b) of the vesicle has become of sufficient thickness to allow 
a distinction between the outer and inner contour; but still we fear it is beyond 
the power of the pencil to give any idea of its delicacy. The extent of its 
indentation (Pl. 9, fig. lla) gives an evidence of very strong contraction, by far 
more intense than has been known to happen in eggs of a smaller size. But 
what must be the infinitesimal minuteness of the particles composing the con- 
tents of this vesicle, when such powerful contraction only produces clusters of 
granules (fig. Ilb, a) almost unrecognizable with a magnifying power of five hun- 
dred diameters! 
The large size to which the Purkinjean vesicle has now attained renders its 
extraction an easy matter, when it has been hardened by boiling; and in this 
state it may readily be preserved in alcohol. Even the vesicle taken from an 
egg one fifth of an inch in diameter, after it has been boiled, may be put up in 
