76 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 then becomes continuous with a tubule, which 

 has already been visible in many sections surrounded by 

 kidney blastema, and which, though not so much branched 

 as the 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 

 dilatations 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. 



In this section the lateral walls of the dorsal part of the 

 dilatation of the 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 (fig. 23), 



