BREEDING HABITS OF THE OPOSSUM HARTMAN. 363 



Plate 8. 



Fig. 33. 65-celled vesicle showing one large entoderm mother cell leaving its 



place in the wall. X00O. 

 *Fig. 34. Somewhat more advanced vesicles (shown in greater detail in fig. 



35). X8. 

 *Fig. 35. Detail of egg shown in figure 34. The thinning of the wall of vesicle is 



apparent. Photographed alive. X82. 

 *Fig. 36. 1 mm. vesicles. A section of one of these is shown in figure 37. XS. 

 Fig. 37. Section of 1 mm. vesicle showing shell memhraue, remnant of albumen, 

 ectoderm, and entoderm. 



Plate 9. 



Fig. 38. Detail of an egg, shown photographed alive in figure 41. The primi- 

 tive streak is indicated by a tongue-shaped shadow. X16. 

 Pig. 39. Portion of section through embryo of egg similar to that shown in 



figure 38. Three mesoderm cells are shown (one is marked m). 

 Fig. 40. Portion of section through egg shown in figure 3S. There are six or 



seven mesodermal cells. 

 *Fig. 41. Vesicles photographed alive (cf. figs. 38-40). X8. 

 Fig. 42. Embryo near term, with umbilicus and shreds of embryonic envelopes. 

 *Fig. 43. Photograph of primitive streak stage, taken alive. 

 Fig. 44. (from Selenka) embryos in utero. The large vesicles are the allantois. 

 (See text.) 



Plate 10. 

 Fig. 45. Section through four suckled mammae and two unoccupied mammae 



(a). Seen in surface view in figure 46. XI. 

 *Fig. 46. View of pouch with greatly swollen mammae. Reduced. 

 Fig. 47. Skin of pouch with mammae. One pouch young has been removed, one 

 remains attached. These are about 10 days old. 



