KIDNEY IN RELATION TO WOLFFIAN BODY IN THE CHICK. 169 
15 to IT) a blastema of cells is still present, precisely 
similar in its appearance and position with regard to the 
Wolffian duct to the Wolffian blastema seen anteriorly at 
earlier stages, and to the blastema seen in the same region 
at later stages (fig. 12). And this can be traced back to the 
opening of the Wolffian duct into the cloaca (fig. 17). 
To this blastema of cells I have given the name kidney 
blastema ; it is at this stage perfectly continuous anteriorly 
with the hinder Wolffian tubules, the junction between the 
two lying in one of the two sections intervening between 
figs. 14 and 15. I ought rather to say the line of future 
separation, for so far they have been always continuous, 
having developed so. The continuity between the kidney 
blastema {kb) and the hinder part of the Wolffian body 
may be seen in fig. 21, which is taken from a chick of nearly 
the same age as that from which figs. 13 — IT were. 
In this figure the section has passed through the hind end 
of the Wolffian duct and through the kidney blastema, and 
has just shaved the hinder end of the Wolffian body, in conse- 
quence of which the hinder Wolffian tubules are only indis - 
tinctly visible. 
The next change to notice is caused by the appearance of 
the ureter. It arises as a growth forward from the dorsal 
border of the enlarged end of the Wolffian duct. This has 
been generally recognised since Kupffer’s^ account. The dila- 
tation of the hind end of the Wolffian duct occurs in a very 
slightly later embryo than that from which fig. 21 was taken. 
The kidney blastema is now found not ventrally close to 
the body-cavity, but lies dorsal to its former position, just 
internal to the dorsal extremity of the dilated Wolffian duct 
(fig. 20). From this dilatation there grows forward a duct, 
the ureter (fig. 19), on the inner side of which lies the kidney 
blastema. 
The ureter, at this stage, has not a very great extent, and 
is only seen for a few more sections ; in fig. 18, still behind 
the Wolffian body, the ureter is not visible; but the kidney 
blastema occupies a dorsal position, as it did in the posterior 
section in which the ureter was present (fig. 19). 
In tracing it forward it gradually descends and becomes 
continuous with the hind end of the Wolffian body. 
In yet older embryos, in which the ureter is more developed 
and overlaps the hind end of the Wolffian body, the kidney 
blastema has quite broken off from the Wolffian body, and 
invests the anterior end of the ureter, so that in a series of 
transverse sections through a chick at this age we should see 
» ‘ Arch. f. M. Anat.,’ Bd. 2. 
