712 EMILY RAT GREGORY, 



9. 

 10 (between somites 7 and 8). 

 , 6. Beginning of lumen in the tubule 



Somite 8, section 11 (between somites 8 and 9). 

 , 4 (5 — 8 are similar). 



11 (between 9 and 10). 

 4. 

 , 6. End of segmentation. 



Figs. 15 — 17. Cross sections from PlatypeUis embr3-o B II (1) 

 showing pro- and mesonephric bases {j)r.b, mes.h). 

 Fig. 18. Same as Fig. 5. 



Figs. 19 — 26. Cross sections from JPlatypeltis embryo II (1). This 

 is more advanced than the first series and the distinction between pro- 

 and mesonephric tubules is very clear. In some cases they can be 

 seen opening side by side into the body-cavity, in others one funnel 

 serves for both rudimentary tubules. 



Fig. 27. End of right Wolffian duct (d) of an embryo of stage II. 

 Figs. 28—29. Ends of left and right Wolffian ducts (d) of an 

 embryo of stage II. 



Plate 46. 

 Figs. 30 — 39. Cross sections from PJatypeltis embryo B II (1), 

 showing the pronephric welt developed from separate outgrowths 

 (pr.h.l, pr.b.2, pr.h.3, 2)r.h.4), the formation of aortic walls ao and 

 very numerous mitotic figures. 



Fig. 30. Som. 5, sect. 9. Fig. 35. Som. 7, sect. 6. 



Fig. 31. „ 6, „ 1. Fig. 36. „ 7, „ 7. 



Fig. 32. „ 6, „ 9. Fig. 37. „ 7, „ 11. 



Fig. 33. „ 6, „ 10. Fig. 38. „ 8, „ 3. 



Fig. 34. „ 7, „ 5. Fig. 39. „ 9, „ 7. 



Figs. 40 — 47. Cross sections from Platypeltis embryo III (5), 

 somite 7, sections 3 — 10, showing pronephric (pr.t) and mesonephric 

 tubule (mes. t) developing side by side and having separate openings 

 into the coelom. The lacunae of the glomus are seen in each section 

 and in 42 — 44 an aortic branch by which they are fed. 



Plate 47. 

 Figs. 48 — 51. Cross sections of Platypeltis embryo V (2). 



Fig. 48. Combined from sections 1 (left) and 2 (right) of somite 8, 

 shows tubules opening into the coelom (o. t) on either side 

 and lacunae of the glomera. The cells of the tubules are 

 much larger than in earlier series. 

 Fig. 49. Combined from section 18, somite 8 (left), and section 1. 

 somite 9 (right). The increased irregularity of tubules is 

 marked. On the right is an aortic branch (a.b). 



