10 



T. H. BURLEND, 



Segments in italics are those in which the primitive kidney 

 rudiment is most pronounced. 



The accompanying diagram (Fig. B in the text) shows the con- 

 dition of the kidney groove etc. at this stage. 



Embryo C. 



Stained for 45 hours in Boraxcarmine. 



On clearing with xylol I observed 10 or 11 proto vertebrae. 

 Mounted on 7 slides upon which were 36, 36, 36, 36, 36, 42 and 

 43 sections respectively. 



Body begins 1,3. 



Gut begins 1,28; foregut ends 3,4; heart extends from 2,18 to 

 3,2 approximately; neurenteric canal from 6,40 to 7,5. 



On the left side the evagination of the somatic mesoderm begins 

 at 3,35 and is continuous backwards to 4,36, although the connection 

 between outgrowth and mesoderm is not of uniform thickness through- 

 out this distance. From 5,1 to 5,15 the kidney rudiment takes 

 the form of a duct which is solid and distinct from the underlying 

 mesoderm, although it shows visible traces of a close relation with 

 the somatic mesoderm at intervals. The duct appears to end in a 

 few scattered flattened cells between ectoderm and mesoderm. 



(See Plate 1 Figs. 6, 7, 8, 9 and 10.) 



Thus the segments affected are: 



Posterior region of V ?, VI, VII, VIII and anterior end of seg- 



