Dentition of Didelphys. 289 
All the figures represent frontal sections through the upper jaw. 
E denotes the rudiment of the enamel-organ of the second teeth. 
‘ig. 1.—Frontal section through the upper jaw of a young Didelphys 
measuring | centim. from rump to nape. The third premolar with 
the rudiment of the enamel-organ of the second tooth. 
Fig. 2.—The first and second incisors of the upper jaw of a young 
Didelphys 3°2 centim. in length. ‘ 
Fig. 3.—Third incisor of the upper jaw of a young Didelphys 2°5 centim. 
in length. 
Fig. 4.—F oun incisor of the upper jaw of a young Didelphys 3 centim. 
in length. 
Fig. 5 te incisor of the upper Jaw of a young Didelphys 3 centim. in 
ength. 
Fig. 6.—Third premolar of the upper jaw of the 3-centim, stage. 
Fig. 7.—Second molar of the upper jaw of the 3-2-centim, stage. 
Fig. 8.—Rudiment of the successor of the second molar of the upper jaw 
at the 5-centim. stage. 
The figures are sketched with the help of the camera lucida. Figs. 1 
and 8 with Zeiss’s objective D and eyepiece no. 2, reduced by one half ; 
figs. 2-7 with Zeiss’s objective A and eyepiece no, 2, reduced by one third. 
