A SOUTH AMERICAN SPECIES OP PEBIPATUS. 229 



middle of the embryo, and shows the so-called amnion in part and the sup- 

 porting cells {sp. c.) ; fig. 9b is cut through the vesicle behind the region of 

 the embryo, and shows the amnion at its highest development. 



Fig. 10. — Section through an embryo of almost the same age as Fig. 9, 

 probably a little older. The vesicle wall in this case is reduced to a very thin 

 string of protoplasm with a few nuclei embedded in it. 



Figs. 11, 12, 13, 14a and 14b are drawings of solid embryos ; in the case of 

 Figs. 11, 12, and 13, lying in the uterus, which has been split open to expose 

 them; in the case of Figs. 14a and 14b the embryo has been removed from 

 the uterus. All, with the exception of Fig. 14a, have been drawn with a Zeiss 

 A after being made transparent by soaking in benzole. Fig. 14a was drawn 

 when lying in absolute alcohol by refracted light. 



Fig. 11. Stage about the same age as Fig. 8. The embryo is entirely 

 sessile ; there is no sign of a stalk. The embryo measures "16 mm. X 

 •06 mm. 

 Fig. 12. Stage of about the same age as Figs. 9a and 9b. The embryo 

 is shown lying in the vesicle, which is in turn shown lying in the 

 uterus ; both uterus and vesicle having been split open. 

 Fig. 13. A stalked embryo in a vesicle, the vesicle lying in the split 



uterus. Embryo measures "24 mm. long. 

 Figs. 14a and 14b. The same embryo, drawn, the former by refracted, 

 the latter by reflected, light ; Fig. 14a a ventral view, Fig. 14b a side 

 view ; show a vesicle with an acorn-shaped embryo lying within it. 

 The embryo is stalked, the stalk springing from the darker area (so- 

 called embryonic placenta). The embryo measures about '24 mm. 

 across. 

 Figs. 15a, 15b, and 15c. — Three sections through different parts of the 

 same embryo. Fig. 15a is the posterior of the three. Fig. 15b the middle one, 

 and Fig. 15c the most anterior. Fig. 15a shows the primitive streak {pr.), 

 Fig. 15b the clump of cells growing forward from that point, Fig. 15c the 

 commencing mesenteron. 



Fig. 16. — Part of the vesicle wall of an embryo of the same age as Fig. 15, 

 showing the commencement of the formation of the so-called placenta. 

 Fig. 17. — Later stage in the development of the placenta. 



