PLATE 1 



EXPLANATION OF FIGURES 



1 Transverse section of a loop of the small intestine in an 8.5-mm. opossum 

 embryo. Wistar series 16177, section 555. The section shows the relation of 

 the large sinus-like blood-vessels to the intestinal mucosa. A diverticulum of 

 the epithelium is seen in the lower right portion of the section. X 125. 



2 Wax-plate reconstruction of a segment of the small intestine in an 8.5-mm. 

 opossum embryo. Wistar series 16177, sections 553-576. The model shows a 

 freely anastomosing plexus of blood-vessels closely pressed upon the mucosa. 

 X 125. 



3 Outline drawing of the viscera in an opossum embryo a few hours before 

 birth to show the positions of the sections shown in figures 11, 12, and 13. From 

 embryo no. 154. X 18. 



4 Outline drawing of the viscera in a young opossum about three days old 

 to show the positions of the sections shown in figures 14, 15, and 16. From pouch- 

 young no. 156. X 18. 



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