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289 



Kiji-. 7 



Fig. 4. 



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Fi^ 





All the figures represent frontal sections through the upper ja-w. 



E denotes the rudiment of the enamel-organ of the second teeth. 



Fig. 1. — Frontal section through the upper jaw of a voung Didelphus 



measuring 1 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 youDo- 



Didelphys 32 centim. in length. 

 Fig. 3. — Third incisor of the upper jaw of a young Didelphys 2-o centim. 



in length. 

 Fig. 4. — Fourth incisor of the upper jaw of a young Didelphys 3 centim. 



in length. 

 Fig. 5 —Fifth incisor of the upper jaw of a young Didelphys 3 centim. in 



length. 

 Fig. 6. — Third premolar of the upper jaw of the 3-centim. .stao-e. 

 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 iaw 



at the 3-centim. stage. 

 The figures are sketched with the help of the camera lucida. Fio-g. 1 

 and 8 with Zeiss's objective B and eyepiece no. 2, reduced by one half; 

 figs. 2 7 with Zeiss's objective A and eyepiece no. 2, reduced bv one third. 



