160 
ADAM SEDGWICK. 
posteriorly, in the same section with the now complicated 
Wolffian body, a dorsal mass of cells. Gradually travelling 
backwards a duct would appear cut across lying in the 
mass of cells ; further back still we should see no Wolffian 
body, but merely a duct with a mass of cells lying just 
internal to it, placed well dorsal to the Wolffian duct. This 
mass of cells is the kidney blastema ; and the duct is the 
ureter. 
Such would be seen in a chick at the end of the fifth day. 
On the sixth day the ureter grows in length, the kidney 
blastema accompanying it, and enveloping its anterior 
extremity. 
The ureter now dilates at intervals, and the kidney blas- 
tema especially collects round these dilatations. From the 
latter, the number of which I have not determined, the 
kidney tubules grow out. In a chick of the seventh day the 
tubules are just beginning to grow out from these dilata- 
tions. The two posterior tubules are, however, far more 
advanced than the anterior. 
The ureter is now a small duct lying just dorsal to the 
Wolffian body ; except at its anterior extremity, where it 
is rather more dorsal, and is completely surrounded by the 
kidney blastema. 
Almost immediately in front of the hind end of the ureter 
a tubule is given off, which runs dorsalwards and outwards. 
The kidney blastema no longer adjoins the ureter, but is 
disposed round the branches of this tubule. The ureter is 
continued forwards through a considerable number of sec- 
tions, giving off no tubules, and unaccompanied by the kidney 
blastema. It now becomes continuous with a tubule, which 
has already been seen in many sections surrounded by kidney 
blastema, and which, though not so much branched as the 
most posterior tubule above mentioned, is more developed 
than any tubule met with in front. 
The ureter continues as a small duct lying just dorsal to 
the Wolffian body. 
In this embryo (seventh day), travelling forwards, several 
dilations could be made out. The appearance presented 
by such a dilatation in transverse section and its position 
with regard to the Wolffian body, may be gathered from an 
inspection of fig. 22. 
The lateral walls of the dorsal part of the dilated ureter 
are closely applied, the lumen being very indistinct. 
Around the dorsal part of the dilatation the kidney 
blastema is present. 
In the next section, or in the next section but one, either 
