542 
DR, MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
was still at the periphery of the cell. A nucleus resembling that in fig. 226. is seen 
more highly magnified in fig. 227- 
360. This nucleus is the object which in my “Second Series” was traced from a 
spherical into a linear form ; in some stage of which latter state, it appears to corre- 
spond to the “primitive trace” of authors on the ovum of the Bird; and, as then 
shown, it is the rudimental embryo. I then stated it to be the nucleus of a cell 
(/. c., par. 300.) ; and from what has been made known in the present memoir in con- 
nexion with facts recorded in my last, it appears that the same process by which a 
nucleus in one instance transforms itself into the embryo, is in operation in another 
instance where the product does not extend beyond the interior of a minute and trans- 
itory cell. Making allowance, indeed, for a difference in form and size, the descrip- 
tion given of the mode of production of the one, might be applied to the other-|~. It 
was shown (/. c., par. 212.) that in the production of the embryo out of a nucleus, 
layer after layer of vesicles or cells comes into view in the interior, while layers pre- 
viously formed are pushed further out ; each of the layers being so distinctly circum- 
scribed as to appear almost membranous at its surface. The same membranous ap- 
pearance we now find to present itself at the surface of the several layers of a nucleus 
in many situations. See, for instance, the nuclei in the twin cells Plate XXV. figs. 199 
and 201. And I have very often found that layers of incipient cells, arising as they 
do out of a nucleus, appear circumscribed by a membrane. Many instances of this 
kind have been referred to in former parts of this memoir (par. 349 Note.). We saw 
such membranes forming around the incipient cells within the germinal vesicle (Plate 
XXIV. fig. 193.), as well as around those of the so-called “yelk” (Plate XXII. figs. 
162. 164. 165. 167, Plate XXIII. figs. 172 to 176. e.). Farther, in the formation of the 
embryo, it was shown that the new layers of altered nuclei or cells come into view 
around a pellucid centre ; and we now find that a corresponding centre gives origin 
to similar appearances in every nucleus described in the present memoir §. The altered 
nuclei or cells, moreover, of which the layers of the embryo are composed ||, present 
an interior denoting a repetition of the same process. The same finely granular ap- 
t In my “ Second Series” a note was added (l. c., par. 193. Note), admitting the possibility of the nucleus 
in question disappearing by liquefaction, and of a linear object — corresponding to the “primitive trace” of 
authors on the ovum of the Bird — arising in its place. The erroneous statement by authors on “ cells,” that 
the nucleus is absorbed, misled me into that admission ; and I have now to state that I adhere to the opinion 
originally expressed, that the embryo is the altered nucleus of a cell, and that the “ primitive traci*” of authors 
appears to be no other than this same nucleus in a comparatively advanced stage. 
+ It was shown that this mysterious centre is present until it has assumed the form of the cavity, including 
the sinus rhomboidalis, in the central portion of the nervous system. 
§ “ Second Series,” /. c., pars. 197. 209. 212 to 215, Plate VII. figs. 118. 121 A. 121 B. 121 C. 122. 123. 
|| Ibid. pars. 300. 305. Plate VIII. fig. 149. The “ vesicles” represented in this figure, as contained the one 
within the other, seem to have been the membranes with which the several portions of a nucleus may appear 
circumscribed, when resolved into cells. We are now also prepared to understand that in my “ Second 
Series,” the space between the membrane of an outer and the membrane of an inner “vesicle” should have 
appeared to be the place of origin of cells ; and that they should have been first seen on the outer surface of 
the inner “vesicle” or “nucleus” ( l . c., pars. 303. 304.). 
