454 EMBRYOLOGY OF THE TURTLE. Part III. 
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granular forms to those of a larger 
Therefore, since by tracing a series of peculiar cells, from the minutest 
size, which have the readily acknowledged 
characteristics of an egg, there can be no doubt left, that the former are, by nature, 
the same as the latter, we may proceed to describe the several phases of devel- 
opment in all these bodies, as the progressive steps in the growth of the egg. 
The initial form of an egg is a dark, oily looking, granule-like, spherical body, 
(Pl. 8, fig. 1, @,) situated among the interstices’ of the cells of the corpus graffia- 
num. As the latter not only, but even their nuclei, surpass such an egg in size 
by several diameters, it is superfluous to debate the question, whether the egg 
may not be the nucleus of a cell of the generating organ? 
At this period in the life of an egg, there arises the question, not only of its 
origin, but also of that of independent cells; for the former is only one of the 
many variously endowed vesicles by which the animal economy performs its multi- 
tudinous functions. Nay, in fact, it is more: the egg, the animal of one single cell, 
potentially contains the principle of the future phenomena of life; so that the gen- 
esis of an egg is neither more nor less than the genesis of one kind of cells, con- 
taining within themselves the type of all future cell formations. The granule-like 
ege, which we have mentioned as the youngest, is a homogeneous mass, from the 
centre to the surface; the thick outline being not indicative of a wall, but resulting 
from the strong refraction, which has no such definite internal boundary as obtains in 
all membranes around limited contents. But yet it must be acknowledged that the 
superficial particles are determinedly the cell wall, and indeed may have a coherence 
among each other greater than those situated interiorly, yet not of sufficient density 
to produce a refraction so different from the latter as to be recognizable by the 
microscope. There is a warrant for this probability, in known examples on a larger 
scale; the yolk parent or outer cell,—even when it has reached maturity, (Pl. 9, fig. 
lli, a; and Pl. 9a, figs. 36-40, a,) and contains a large nucleus and several nucleoli, 
—shows this plainly, for it is a mass of excessively hyaline granules, the outer of 
which are only a little more coherent to each other than those within, but not 
dense enough to produce a recognizable refraction till water is applied and the con- 
tents burst out; whilst the wall, (Pl. 9, fig. 7c, and Pl. 9a, fig. 7a,) by its greater 
1 The first blood corpuscles are yolk-cell nuclei 
which have undergone changes identical with those of 
the whole “embryo,” and they alone remain free, cir- 
culating in the channels hollowed out in a mass of 
cells identical with themselves. These are the first 
cells originating interstitially, but yet, after all, not 
essentially so, as is the case with the egg; for each 
blood corpuscele is a segment of an original yolk-cell 
nucleus, which has gone through the process of self- 
division; whilst the egg originates just as the pri- 
mary yolk cell does, by conglomeration of particles, 
and the formation of a membrane around the pari- 
etes of this concretion. 
2 See Thompson’s suggestion to that effect in 
Cyclopedia of Anatomy, article Ovum, p. 136, Oct., 
185 
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