362 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



Fig. 6. Thirteen newly-born pouch young (b), five pouch young a week old 

 (c). Above, at a, cross section of mammary gland showing three 

 teats on lower edge occupied tor one hour by the newly -born pouch 

 young. XI. 



* Fig. 7. The generative organs at oestrus, showing greatly swollen lateral 



vaginal canals (1. v. c.) and ripe follicles in ovary (ov.). Ut. 

 uterus. X2. 



Plate 3. 



* Fig. 8. Pseudopregnant organs. Retrogression of uteri has already set 



in XI. 



* Fig. 9. The organs in pregnancy, near term. Slightly reduced. 



Plate 4. 



* Fig. 10. Uterus everted, showing eight vesicles, somewhat more advanced 



than the egg shown in Figure 13. XI. 



* Fig. 11. Open uterus No. 560', showing vesicles containing embryos with 



8-10 somites; 18 hours later than egg shown in Figure 13. 



* Fig. 12. 9 vesicles within a bag made of the uterine mucos. XI. 

 Fig. 13. One egg of batch No. 560 (cf. fig. 11). X8. 



* Fig. 14. Twelve 4-celled eggs, No. 293. The white spot in center is the " yolk " 



or ovum proper. XS. 



* Fig. 15. Sister eggs to batch 293 (fig. 14), 83 \ hours later. X8. 



Plate 5. 



* Fig. 16. Three normal vesicles, one abnormal vesicle and seven unfertilized 



eggs. No. 585. X8. 



* Fig. 17. Embryos 585', five days later. XI. 



* Fig. 18. Eggs No. 561. X8. 



* Fig. 19. Embryos 7* days later, No. 561'. XI. 



Plate 6. 



* Fig. 20. Young vesicles No. 582. X6. 



Fig. 21. Two vesicles No. 582' with embryos, 2| days later. These are two 

 of the vesicles shown in Figures 24 and 25. X2£. 



* Fig. 22. The surviving uterus of No. 582 . Xf. 



* Fig. 23. A similar stage with the musculation cut away leaving only the 



mucosa. The bulging vesicles may be seen. Xf. 



* Fig. 24. The uterus of No. 5S2 opened, showing vesicles in situ. X f. 



* Fig. 25. The same. The eggs are floated out to show the depressions in the 



mucosa ("implantation sites") made by the vesicles. Xf. 



Plate 7. 



Fig. 26. Section through a 4-celled egg. Note extruded yolk about the cells. 

 X200. 



Fig. 27. 30-celled egg. The hollow vesicle is in process of formation. Yolk 

 within the partially completed vesicle. X200. 



Fig. 28. Ovum in stage of young vesicle (center) with concentric layers of 

 albumen about it. 8m, shell membrane (shrunken). X125. 



Fig. 29. Opossum egg showing an Ascaris egg (a) embedded in the albumen. 

 *Figs. 30, 31, and 32. Three double-yolked eggs at various stages of develop- 

 ment (arrows). 



