294 Mr A. Sedgwick, On the development of the kidney [Nov, 24, 



the Wolffian tubules are developed from S-shaped strings of 

 cells, continuous with the epithelium of the body-cavity, such as 

 Kolliker has figured on p. 201 of his Development of man and 

 the higher animals. Posteriorly, from the 20th segment back- 

 wards, this is not the case. 



In this region before the appearance of tubules, there may 

 be seen in longitudinal sections or in a series of transverse sections 

 a continuous cord of cells, separate from the peritoneal epithelium, 

 lying just internal to the Wolffian duct, extending as far back 

 as the opening of the Wolffian duct into the cloaca. 



This cord of cells developes continuously from before backwards 

 from the intermediate cell mass. Almost directly after its ap- 

 pearance, it begins to break up in front into a series of primary 

 Wolffian tubules ; and this process is continued gradually back- 

 wards as far as the 80th segmeut. Here the process stops. From 

 the 80th segment to the 84th, which is about the position of the 

 opening of the Wolffian duct into the cloaca, the cord of cells 

 does not at this stage break up into tubules. There is in fact 

 a break in the continuity of development. The part of the cord 

 behind the 30th segment gives rise at a later period to the 

 tubules of the permanent kidney. Till about the end of the 

 fourth day this part of the cord does not undergo any marked, 

 changes, but remains continuous with the part of the Wolffian 

 body in the 80th segment, in which secondary and tertiary tubules 

 early make their appearance. 



At about this stage (end of 4th day) the ureter appears as 

 a dorsal diverticulum of the Wolffian duct, close to its opening 

 into the cloaca. With the appearance of the ureter, the cord 

 of cells begins to move dorsalwards. In consequence of this 

 change of position, which proceeds rapidly, its anterior end ceases 

 to be continuous with the Wolffian body, and never again comes 

 into connection with it. The ureter as it grows forward occupies a 

 position just external to this cord of cells, and the two together grow 

 forward dorsalwards, overlapping the hind end of the Wolffian body. 

 Eventually this forward growth becomes much more considerable. 



Meanwhile, the ureter dilates at intervals ; the cells of the cord 

 increase largely at these points, become continuous with the wall 

 of the duct, and eventually give rise to the tubules of the kidney. 

 I do not propose now to go into the exact details of the de- 

 velopment of the kidney tubules ; an account of this I reserve 

 for a more detailed paper, with figures, which I hope shortly to 

 publish. I will content myself with saying that my observations 

 have led me to the conclusion, in opposition to the results which 

 Kolliker^ and Lowe^ have arrived at for Mammalia, that the 



^ EnhvicHungsgeschichte des Menschen u. der hoheren Thiere. 

 ^ Centralblatt filr die med. Wisseiiftcliaften, Oct. 1879. 



