239 
ova of the Opossum tribe. 
Plate XVII. 
Ovarium of the American Opossum. 
Fig. 1. Front view of the ovarium of the large American 
opossum : natural size. 
Fig. 2. The same view, magnified five diameters. 
Back view, magnified five diameters. 
A perpendicular section, magnified five diameters 
The same section, magnified ten diameters. 
A young yelk-bag, magnified twenty diameters. 
A full grown yelk-bag, magnified twenty dia- 
Fig. 3. 
Fig. 4. 
Fig. 5- 
Fig. 6. 
Fig. 7. 
meters. 
Fig. 8. 
A full grown yelk-bag opened, to show its con- 
tents ; magnified twenty diameters. 
Plate XVIII. 
Ovarium of the Ornithorhynchus Paradoxus. 
Fig. 1. Front view of the ovarium of the ornithorhynchus 
paradoxus : natural size. 
Fig. 2. The same view, magnified five diameters. 
Fig. 3. Back view, magnified five diameters. 
Fig. 4. A small portion cut off from the upper end of the 
left side of Fig. 3. ; magnified ten diameters. 
Fig. 5. An internal view of the same portion, magnified 
ten diameters, to show the yelk-bags. 
Fig. 6. A full grown yelk-bag, magnified twenty dia- 
meters. 
Fig. 7. A young yelk-bag opened, to show its contents : 
magnified twenty diameters. 
Fig. 8. A full grown yelk-bag opened, to show its con- 
tents : magnified twenty diameters. 
