KIDNEY IN RELATION TO WOLFFIAN BODY IN THE CHICK. 11 



either backwards or forwards, the dorsal dilatation would be no 

 longer visible, but, occupying the position of the dorsal part 

 of the dilatation, would be seen a tubule surrounded by the 

 cells of the kidney blastema. 



In the next section to this (fig. 24) the walls of the tubule 

 become indistinctly marked off from the kidney blastema. 

 Some of the large columnar cells of the kidney tubule become 

 branched, the processes being continuous with the processes 

 of the branched cells of the kidney blastema. In fact, every 

 stage of cell shape between a columnar lining cell of the 

 tubule and a branched cell of the blastema is visible. 



The lumen of the tubule is no longer distinct, it not being 

 possible to say what is an intercellular space and what the 

 lumen of the tubule. 



In the next section no trace of a tubule is visible, its 

 place being occupied by the cells of the blastema. 



Fig. 23 is taken from a section next but one to fig. 22. 

 Nine such dorsal dilatations of the ureter, with commencing 

 tubules growing from them, could be made out in the embryo 

 under consideration. 



In front of the anterior dilatation the tubules open directly 

 into the ureter which in this region has become more dorsal 

 with regard to the Wolffian body. Tubules in this region, more- 

 over, are given off from the ventral side of the ureter, corre- 

 sponding almost exactly to those given off from the dorsal side. 

 Four pairs could be made out ; after which the ureter ended 

 closely surrounded on all sides by dense kidney blastema. 



The next and last stage, which I have closely examined, 

 was in an eight-day chick. The kidney had reached a great 

 complication of structure. Malpighian bodies had, however, 

 not distinctly appeared. The tubules were still surrounded 

 by kidney blastema which was especially conspicuous at their 

 growing ends. The appearance of the latter, which was ex- 

 actly similar in all essential details to the growing points of 

 the tubules of the stage last described, is represented in fig. 24. 



Before considering the bearing of the above facts upon the 

 questions asked at the outset, I will recapitulate the more 

 important points in the development of the Avian kidney 

 and Wolffian body. 



1. The cells which give rise to the Wolffian and kidney 

 tubules do not develop as involutions of the peritoneal epi- 

 thelium, but from a blastema of cells derived from the inter- 

 mediate cell mass. 



2. The blastema of the kidney is at first perfectly con- 

 tinuous with that of the Wolffian body, and cannot be dis- 

 tinguished from it, 



