ME. JONES ON THE IMPREGNATED MAMMIFEROUS OVUM. 
345 
formed ; it has extended itself so as to close in the white spot. Evolution then pro- 
ceeds. 
The change which takes place in the yelk of the bird’s egg appears to be limited to 
the neighbourhood of the cicatricula. In the ovum of the mammifera, there being 
little more than a blastoderma to be formed, the whole of the vitelline grains undergo 
a change, and are resolved into a vesicular blastoderma, presenting the same peculiar 
friable and globular texture as the blastoderma of the egg of the Newt, Frog, Bird, &c. 
The matter contained in the cavity of the yelk of the bird’s egg seems to be a sub- 
stance of the same nature as the blastoderma, and to serve for the extension of it. 
The blastoderma of the bird’s egg being once formed by the effusion of the fluid of 
the vesicle of Purkinge, and animated by fecundation, probably has the power to 
assimilate the matter in the cavity of the yelk to its own substance, without the assist- 
ance of a fluid such as that of the vesicle of Purkinge, which was first required to 
promote its formation. There is no central cavity in the ova of the Frog and Newt, 
because the blastoderma is formed at once all round the ovum. 
Description of the Plate. 
PLATE XVI. 
Fig. 1. An ovum found in the Fallopian tube of a Rabbit the third day after im- 
pregnation ; magnified forty diameters. 
Fig. 2. The ovum of the Frog when recently laid ; magnified two diameters. 
Fig. 3. The ovum of a water Newt in which development has commenced ; mag- 
nified rather more than twice. 
Fig. 4. A diagram showing the embryo of the Newt after the vitellary membrane 
has given way, contained only within the cavity of the substance which is added to 
the ovum in the oviduct. 
Fig. 5. A diagram showing the embryo of the Frog still surrounded by the vitellary 
membrane as well as the gelatinous substance tvhich is added to the ovum in the 
oviduct. 
Fig. 6. An ovum found in the horn of the uterus of a Rabbit seven days after im- 
pregnation ; magnified forty diameters. 
Fig. 7- A human ovum aborted at the third or fourth week ; natural size. 
Figs. 8, 9, 10. Bodies found in the right Fallopian tube of the Rabbit which forms 
the subject of observation 1 ; magnified about fourteen diameters. 
Fig. 11. This exhibits the breaking up into crystalline forms, observed on the sur- 
face of the Frog’s ovum after impregnation ; magnified about six diameters. 
Fig. 12, 13. Diagrams illustrating the mode of disappearance of the germinal 
vesicle. 
