PLATE 5 



EXPLANATION OF FIGURES 



41) From a frontal section of a 4.5 mm. embryo (about 25 somites). The aniage 

 of the duct is beginning to grow back from the pronephros and has just become at- 

 tached to the ectoderm, which is much thinned and bent outward just above the 

 point of attachment. 



50 From a frontal section of a 5 mm. embryo, shows the close contact of ecto- 

 derm and the aniage of, the duct, and demonstrates the impossibility of distinguish- 

 ing between the layers, were the limiting membrane invisible. 



51 to 54 Frontal sections of 5.5 and 6 mm. embryos, demonstrating the char- 

 acter of the growing tip of the aniage of the duct . 



55 to 60 ' Showing mitotic figures in duct and ectoderm. Figure 56 is in the 

 terminal cells of the aniage of the duct. Figures 57, 58 and 60 are comparable to 

 the figure of Van Wijhe. The mitotic cells in the ectoderm are about to divide 

 and, but for the limiting membrane, they might be interpreted as contributing 

 cells to the aniage of the duct. This is especially evident in figure 57. Figure 58 

 shows the same section after the aniage has separated from the ectoderm and has 

 been moved back into place, showing the entire independence of duct and ecto- 

 derm; figure 60 is much the same. 



61 From a frontal section of a 7.5 mm. embryo, shows the flisproportion in 

 size between the aniage of the duct and the ectoderm. It also shows that the 

 ectoderm may be modified at other points than at the growing tip. The close re- 

 lation between duct and ectoderm and the limiting membrane are also shown. 



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