DEVELOPMENT OF KIDNEYS AND FAT-BODIES IN THE FROG. 143 



surrounding parts, this tube shifts its relations, and in place of running 

 directly outwards, runs forwards, outwards, and downwards round 

 the anterior border of the root of the lung, ending with a backwardly 

 directed mouth, which opens into the body cavity below the lung. 

 Still later, the greater part of the length of this tube opens out 

 by separation of its lips, and becomes once more a groove, which 

 gradually flattens and ultimately disappears altogether, while its 

 dorsal end opposite the root of the lung becomes the permanent 

 mouth of the oviduct. 



The hinder end of the Miillerian duct grows backwards, according 

 to Hoffmann, quite independently of the Wolffian duct, to the outer 

 side of which it lies, but in very close connection with a longitudinal 

 strip of peritoneum, the cells of which are columnar in shape. The 

 actual mode of growth of the duct was not observed, but Hoffmann 

 is inclined to regard is as effected at the expense of the strip of 

 peritoneal cells. 



Of the above account by Hoffmann we can confirm certain 

 portions. 



In a tailed frog, such as that shown in Fig. 5, the part of the 

 archinephric duct between the head kidney and the Wolffian body 

 is extremely slender, and at places its lumen is entirely obliterated. 

 We have, however, not seen any division of this duct into Wolffian 

 and Miillerian ducts at this stage. Further back, on entering the 

 Wolffian body, the duct becomes much larger, and has a conspicuous 

 lumen. 



In a frog at the end of the first year we find the head kidney almost 

 obliterated and completely separate from the duct; all three nephro- 

 stomes have disappeared completely. The Miillerian duct is well deve- 

 loped at its anterior end, which runs, exactly as Hoffmann describes 

 it, almost vertically downwards round the outer border of the root 

 of the lung, and then backAvards for a short distance along its ventral 

 surface, ending with an open mouth into the body cavity, placed a 

 short distance below the level of the pulmonary vein. We can, 

 therefore, confirm Hoffmann's statements that in the frog the 

 abdominal opening of the Miillerian duct is not formed from one of 

 the nephrostomes, and that in a young frog the Miillerian duct at 

 first extends round the root of the lung and opens on its ventral 

 surface. 



