288 J. B. Haycraft, 



Another point that we may notice in passing is the fact that in 

 every section of a young Kidney we get what appear to be isolated 

 masses of epithelial cells: such a mass is seen in a to the right hand 

 of X. Is it not possible that this appearance led many observers to 

 believe in the independent origin of the convoluted tubule and its 

 subsequent junction with the collecting tubules; and may it not be 

 that Balfour was influenced in his description of the formation of the 

 tubules by the same appearance? At any rate the explanation of the 

 appearance is quite easy, by the help of serial sections it is seen to 

 be due to the plane of section passing through the epithelium of a 

 tubule above or below the lumen of the tube. The isolated mass in 

 a is seen in lower sections {b and c) to form part of the tubule 

 which in a apparently terminated at the point X. Although some 

 hundreds of sections, taken from embryo rabbits ranging from the 

 11th day (at which the Kidney first appears) to birth, were carefully 

 examined I have never seen isolated masses of epithelial cells which 

 were really isolated in the blastema and did not form part of urinary 

 tubules. 



Remak's and Kölliker's view^ is confirmed. 



It therefore appears to me that the evidence in favour of the 

 view that the urinary tubules are formed by the Kidney blastema, is 

 unsupported by facts, and it will subsequently be shewn that there 

 is strong evidence in support of the opinions held by Remak and 

 Kölliker that the tubules throughout their entire length are branches 

 from the ureters, and that their epithelial cells are descendants of the 

 cells lining the Wolffian duct: in this case the Kidney develops on 

 the same lines as an ordinary secreting gland. Balfour and others 

 have maintained that the tubules of the Wolffian body arise indepen- 

 dently and then join the Wolffian duct and this similarity of deve- 

 lopment to that which they supposed occurred in the Kidney, was a 

 point upon which very especial stress was laid. As far as I can make 

 out however this description of the Wolffian body is also at fault and 

 the tubules are from the first (in the chick and rabbit at any rate) 

 connected with, as outgrowths of, the Wolffian duct. As my mate- 



