Cuap. I. DEVELOPMENT OF THE YOLK CELLS. 465 
the hyaline masses swell slightly, and the imternal portions lose their homogeneity : 
multitudes of faint granular particles appear suddenly; they dance about their con- 
fined sphere in a zigzag quiver, and finally their delicate boundary wall, which 
by this time has become unequivocally demonstrated, bursts suddenly on one side, 
and extrudes at a single contractive effort nearly the whole horde of its vivacious 
motes, assuming itself by this loss a wrinkled, unsymmetrical, much diminished 
shape, but still holding a few oscillating corpuscles. It may yet, perhaps, be 
doubted that there is a cell wall, according to the usual acceptation, embracing 
these homogeneous globules of albumen; for the envelope just displayed soon falls 
and crumbles to atoms, identical apparently with those which not long before 
rushed from its embrace, whilst a genuine cell wall, so called, disintegrates only 
under the process of decay. This, however, is only a matter of degree after all: 
both fall to atoms; the former soon, by reason of its undeveloped nature; the 
latter holds out longer, because of the greater adherence of its component par- 
ticles. Moreover, on account of its very slightly changed density and refraction, 
the former is not recognizable as a separate layer from the mass within; whilst 
the latter is differentiated by the great predominance of these two features, which 
are lacking in the young cell. 
Here, then, we have essentially, nay, m every sense, a cell, a hollow layer of 
spherical surface, derived from the lateral adherence of the superficial particles of a 
homogeneous globule" It is not a cell formation by the hollowing out of a 
solid substance, forming at first a very thick wall, which would stretch by the 
increase of the contents, as it gradually surrounds a larger space, till it thins 
out to the ordinary crassitude of such envelopes. Never, throughout the whole 
range of cell development in the egg, is there the merest hint at this mode of 
oo? 
genesis. From the beginning to the end of the growth of the ectoblast it 
ever preserves the same thin stratum, apparently of a single layer of corpuscles, 
and moreover the same tenderness and the same refracting power. Nor can we 
compare this process to the received mode of cell origin, according to which a 
wall is condensed around and upon a “nucleus,’? for the mesoblast is often absent 
as for its envelope. 
1 See p. 454, on the primary cell wall of the yolk. An incipient ectoblast is a homo- 
2 Since the word nucleus implies a body around 
which something condenses, and nothing of the kind 
takes place here, the name mesoblast is certainly a 
much preferable designation for that part of the cell 
which is commonly called nucleus. The new names 
proposed here for the parts of a cell have the further 
advantage, that they may be applied for the whole 
body which they are intended to designate, as well 
5 
509 
geneous mass, which afterwards has an envelope dis- 
tinet from its contents, and so is the mesoblast ; even 
the entoblasts may become vesicular and contain one 
or more entosthoblasts. It is therefore desirable that 
the nomenclature of the cell should be applicable to 
these different stages of its development, which the 
names of cell, cell wall or cell contents, nucleus and 
nucleolus, are not. 
