Dr Barry's He searches in Embryology. 139 



in a state very different from that in which it leaves the ovary ; 

 hence the opinion that " in their passage through the tube the 

 ova of Mammalia undergo scarcely any metamorphosis at all," 

 is erroneous. Among the changes taking place in the o\Tim 

 during its passage through the Fallopian tube are the follow- 

 ing, viz. 1. An outer membrane, the chorion, becomes visible. 

 2. The membrane originally mvesting the yelk, which had 

 suddenly thickened, disappears by liquefaction, so that the 

 yelk is now immediately surrounded by the thick transparent 

 membrane of the ovarian ovum. 3. In the centre of the yelk, 

 that is, in the situation to which the germinal vesicle retiu-ned 

 before the ovum left the ovary, there arise several very large 

 and exceedingly transparent vesicles : these disappear, and 

 are succeeded by a smaller and more numerous set ; several 

 sets thus successively come into view, the vesicles of each suc- 

 ceeding set being smaller than the last, until a mulberry-like 

 structure has been produced, which occupies the centre of the 

 ovum. Each of the vesicles of which the surface of the mul- 

 berry-like structm-e is composed contains a pellucid nucleus ; 

 and each nucleus presents a nucleolus. 



In the uterus a layer of vesicles of the same kind as those 

 of the last and smallest set here mentioned makes its appear- 

 ance on the whole of the inner surface of the membrane 

 which now invests the yelk. The mulberry-like structure 

 then passes from the centre of the yelk to a certain part of 

 that layer (the vesicles of the latter coalescing with those of 

 the former where the two sets are in contact to form a mem- 

 brane), and the interior of the mulberry-like structm-e is now 

 seen to be occupied by a large vesicle containing a fluid and 

 granules. In the centre of this vesicle is a spherical body 

 having a granulous appearance, and containing a cavity appa- 

 rently filled with a colourless and pellucid fluid. This hollow 

 spherical body seems to be the true germ. The vesicle contain- 

 ing it disappears, and in its place is seen an elliptical depres- 

 sion filled with a pellucid fluid. In the centre of this depression 

 is the germ, still presenting the appearance of a hollow sphere. 

 The germ separates into a central and a peripheral portion : 

 the central portion occupies the situation of the future brain, 

 and soon presents a pointed process which is the rudiment of 



