DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
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mode, the period, or the place of origin of the new being ; or indeed to understand 
the ovum in any of its future phases. 
341. In Plate XXIII. fig. 169. is an ovum of 5^ hours, in which the germinal 
vesicle was apparently undergoing this change of place ; a change which appears to 
me sufficient in itself to show that an ovum has undergone fecundation'!'. The vesicle 
had begun to regain its globular form. The point of fecundation, however, was still 
visible at the periphery ; whence, and from the unclosed state of the fissure in the 
membrane f 3 I am disposed to think the ovum had not been long fecundated, for the 
point of fecundation is subsequently seen to occupy the centre of the germinal vesicle, 
as was the case in the ova, figs. 1/1. 173. 174. 180.; and soon after fecundation the 
orifice in question is no longer seen. 
Changes in the Substance by which the Germinal V esicle is surrounded. 
342. In the ovum fig. 170. the germinal vesicle, having receded from the surface 
into the interior of the ovum, had become closely surrounded by a layer of cells, 
each of which presented a remarkably opake nucleus^. Subsequently this nucleus 
seems to resolve itself into cells, and the same origin of new cells appears to take 
place in its interior, as that which I have described in a former page (par. 326 to 
328.). 
343. It appears also that new layers of cells come into view internal to the layer 
just described ; when a succession of the same changes takes place as those already 
mentioned. Layer after layer of cells makes its appearance in the interior, — often 
seen to have become circumscribed by a proper membrane (e), — while cells occupy- 
ing a more external situation undergo liquefaction. (See the explanation of figs. 170 
to 176.) 
f I quote the following from a high authority. “ Difference between the fecundated and unfecundated ovum . — 
In the first place, in reference to this subject, it would be interesting to know whether any material difference 
exists between the structure of the fecundated and unfecundated egg. Did any difference of structure exist, we 
should he disposed to look for it first in that part of the egg which is more immediately connected with the 
new being, viz. in its germinal portion ; but we regret to say that the investigations of naturalists have not as 
yet pointed out any marked difference in a satisfactory manner. Nor can we with certainty fix on what part of 
the egg the influence of the male semen more immediately operates. Since the foetus grows from the centre of 
the germinal layer, it has been commonly supposed that this is the part of the egg which is most immediately 
effected by fecundation, hut we know nothing of this ; and it might be held on the other hand, that the effect 
of fecundation operates on the rest of the contents of the egg in enabling them to be assimilated round the 
germinal centre or rallying point of the development of the new being.” Allen Thomson, in Dr. Todd’s 
Cyclopsedia of Anatomy and Physiology, Article “ Generation,” pp. 462 and 467. 
I In the ova, figs. 170. 171., the situation of the germinal vesicle was not quite central. The cells sur- 
rounding it in these figures correspond apparently to the ellipsoidal mass figured in my “ Second Series” (7. c., 
Plate I. figs. 96 and 97.), as seen with a lower magnifying power. 
