354 DR D. BEKRY HART. 



They occupy the greater part of the length of this cavity, reach- 

 ins from the heart, downwards and backwards, to the caudal 

 extremity. As is well known, we have, in the lower vertebrates, 

 these bodies consisting of two parts — the pronephros or head 

 kidney, and mesonephros or Wolffian body proper. In the human 

 embryo it is disputed as to whether the pronephros is really 

 represented. In my specimen of a month old I found at the top 

 of the "Wolffian body a pit with a small tubule at its deep end, 

 and this seemed to me to be pronephric in its nature (figs. 32 

 and 33). It was, at any rate, the only part of the Wolffian body 

 which had a free peritoneal opening for its tubule. Another 

 view would be, of course, that it is the beginning of the duct of 

 Muller. 



In the lower mammals we get very instructive examples of 

 the minute anatomy. I have examined this in several speci- 

 mens of the chick, and rabbit, and pig embryo (many specimens 

 in serial transverse and longitudinal section), and found Minot's 

 description correct. The mass of its substance is made up of 

 tubules lined with epithelium, and opening towards the surface 

 of the organ into the Wolffian duct. At the other end of the 

 tubule is a Malpighian corpuscle with a thin lining of epithelium 

 — the capsule of Bowman. We have no exact information as 

 to the mechanism of their excretion, but they are evidently 

 analogous in their function to the permanent kidneys. 



Along the outer free peritoneal surface of the Wolffian body 

 runs the WoltKan duct, the collecting tubules opening into it 

 (fig. 34 ; vide also Kollmann, p. 399). The Wolffian duct opens 

 below into the urinogenital sinus (figs. 11 and 12). 



The Milllerian ducts in embryos of 7-13 mm. develop at the 

 fifth week as peritoneal involutions on the lateral aspects of the 

 Wolffian bodies, running first to their outer edge and then to 

 the inner surface. They course down and back in close relation 

 to the Wolffian duct, and ultimately end blindly on the back of 

 the urinogenital sinus, immediately above the Wolffian duct 

 openings, and form there the eminence of Muller (fig. 11). The 

 Milllerian duct, as Sedgwick long ago asserted, I consider to be 

 probably of pronephric origin, for reasons to be afterwards given. 

 Gregg Wilson's papers may be referred to for a summary on 

 this point. 



