344 Agassiz on the Limbryology of the Turtle. 
the development of distinct yolk cells, the yolk passes through 
some peculiar granulated phases, the most remarkable of which 
is the gradual encroachment of granules, commencing at one 
side of the egg, upon the hitherto homogeneous contents, till 
they pass across the whole bulk of the vitellus. At one time, 
during this progressive incursion of the granules, the egg appears 
as if a half of two different eggs had been stuck together, one- 
half being homogeneous and the other thickly granulated. After 
the granular stages, at the time the egg is about one-sixteenth of 
an inch in diameter, the oily looking granules gradually disap- 
pear and at the same time minute hyaline, albuminous, vesicular 
bodies begin to develop. These again, as is the case with the 
egg-cell and Purkinjean vesicle, originate without the interven- 
tion of a so-called nucleus,* and each one grows for some time 
without the least sign of a second body within its wall. 
‘Here then we have essentially, nay in every sense, ll, 
hollow layer of spherical surface derived from the lateral adhe- 
rence 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 
egg, is there the merest hint of this mode of genesis. From the 
_ * “Thus far we have employed, in our descriptions of the egg and its cones 
the nomenclature generally in use to designate its different parts, and those 0 
cell. But this cite Pee respecting th 
mode of formation and the functions of these parts, is completely theoretical in 
we are about to consider more 
ng. : : 
fully the origin and successive growth of the ve cells, to discard every techiical 
ich we 
ne ries w 
is intended to express, These parts are therefore designated in the a by be 
wing names: ectoblast is applied to the outer envelop; mesoblast A 
nucleus; entoblast to the sb nucleolus; and, when this contains & stil 
y, this is called entosthoblast. 
the nomenclature of the egg, similar objections may be raised against tit 
inative vesicle and dot, as neither of the has them, 
est reference to the formation of the g all therefore desi d Wagne- 
h as some embryo do, by the names of the mth the cell 
rian vesicles. Applying our nomenclature to a comparison of the egg with | a 
the Montiges: i is to be considered as an agian oa Purkingean para 
