Cap. II. THE WHOLE EGG IS THE EMBRYO. 539 
cells among each other, and their resemblance to those of an unfecundated egg 
SS? 
provided we are aware that the changes which it undergoes in its earlier growth 
essentially belong to a period anterior to the final influence fecundation has upon 
its development. 
As soon as it is once admitted that the so-called nutritive yolk, as contrasted 
with the embryo, is an essential part of the embryo itself, there is no longer 
any possibility of tracing a distinction between an embryo, as it stands out from 
the yolk at a later period, and the yolk, as embryo, before any morphological 
difference is introduced between the two, their differentiation being clearly the 
result of a continuous process, initiated very early in the youngest ovarian eges 
prior to the first copulation. It follows, therefore, that the egg itself is, in the 
strictest sense of its physiological importance, a new being, an embryo, originat- 
ing in the ovary as a single, specific cell; and that, from its earliest appearance, 
it is to be considered as the new animal in progress of formation. From this 
point of view, the names egg, embryo, young and adult animal, are only conven- 
‘Oo? 
ient appellations to indicate the different periods of growth of one and the same 
being. 
Thus far, we have limited our remarks to facts which are within the reach 
of our investigations. But the inquiring mind is unwilling to stop at the limits 
assigned to its progress by the circumstances of the moment. May we not ask, 
therefore, what takes place at the time when an egg, the germ of a new being, 
originates? Apparently it is only a concentration of an exceedingly small mass 
of oleagino-albuminous substance, in the form of a sphere. But, in reality, it must 
be a very different thing; for that sphere is, from the beginning, the centre of an 
action that differs from the functions gomg on in any other part of the parental 
organism. It is alive, and at once proceeds to develop, in a regular manner, 
towards a definite end. From the beginning it assimilates to itself, and for its 
own ends, the material supplies it receives from without. Whatever may be said 
to the contrary, a principle of life is now at work in the egg which is totally 
shapes the layers of its more superior portions into as in Mammals, Birds, and the scaly Reptiles,—or, as 
the cerebro-spinal systems of organs of the body, as happens in some Batrachians, according to Wyman, 
any other portion; or that it is in fact an organ in pro- coiling very early into an intestine, —or, as Remak 
gress of development, and more or less permanent, has shown in Rana esculenta, moulding itself at 
according to the animal in which it originates. In- 
deed, we are inclined to believe, that, upon further 
investigation, this portion of the body will be found 
never to disappear entirely, but only to assume suc- 
cessively various guises, either diminishing its bulk 
and rotundity and lengthening out into the intestine, 
first into a thick cylindrical digestive canal, which 
subsequently lengthens and becomes coiled at the ex- 
pense of its own thickness, — or simply lengthening, 
and at the same time diminishing its transverse diam- 
eter, as in Abramis (Cyprinus) Blicea (Baer, Ent- 
wickel. der Fische, ete., q. p. 81: fig. 9-20.) 
