Text-fig. ].5.' 



"^'■j^^ "" ^"''^ ■'■■■ ' '' • ■ 



'T-'/ . 







r<^' v. 



K.2.: 







Section throug-h tlie ri<;bt posterior i-egion of an eniVjryo in the 

 same stage as figs. 1 and 2 of PI. '11. showing tlie ectoderm 

 cells, K. 2, which will form the secondary kidney, still lying on 

 the sni"face. 



Text-fig. 16. 



'-<? 





St.. 



hgld. 



Ka 



A\c 



Section through the same region of an embryo a few hours older. 

 ^ Text-figs. 15-20 are drawn from sections 3 ^ thick, with an Abbe 

 camera with y ^ oil-immersion and a compensating eye-piece. Zeiss, No. 8, 

 except Text-fig. 20, which is much less highly magnified. N.B. — For 

 signification of the lettering of figs. 15 to 20 see the explanation of the 

 same letters in PI. 22, given on p. 539. 



