1891.] of the Oviduct in the Frog. 149 



nephrostome of the pronephros. This patch, he says, is dorsally 

 involuted to form a groove, open below. Ventrally it is prolonged 

 downwards and outwards over the surface of the pronephros, and 

 even beyond it for a short distance. It is distinguished from the 

 unmodified epithelium by being highly columnar. The part of 

 the Wolffian duct in front of the mesonephros, the lumen of which 

 is at this stage much reduced, then separates itself from the de- 

 generating pronephros, and splits into two rods of cells. The 

 dorsal of these is continuous with the Wolffian duct behind, and 

 the ventral one applies itself in front to this involuted patch of 

 peritoneum, and forms the first rudiment of the oviduct. But the 

 oviduct does not grow back in continuity with the Wolffian duct. 

 On the contrary, it enters into close connection with a longitudinal 

 strip of peritoneum which lies to the outer border of the kidney, 

 and consists of columnar epithelium. Hoffmann states that the 

 hinder portion of the duct is formed from these cells, though 

 whether by involution to form a groove or by proliferation he 

 could not determine. In the meantime, the groove which formed 

 the ostium of the duct, and which was originally dorsal, has 

 become prolonged ventrally round the base of the lung. It closes, 

 forming a canal which now opens ventrally. Later, this ventral 

 extension atrophies, leaving the ostium in its original dorsal 

 position. 



Marshall and Bles have only observed a few isolated facts in 

 the development of the oviduct. They confirm Hoffmann in his 

 account of the ventral displacement of the ostium ; but fail to 

 observe any splitting of the front part of the Wolffian duct. They 

 state that the hind end of the duct is, in the first year, a solid rod 

 of cells ; but do not notice any relation to the peritoneum. 



My observations differ from those of Hoffmann in several im- 

 portant particulars. It will be convenient to describe first the 

 origin and fate of the abdominal opening, and then that of the 

 rest of the duct. In a tadpole in which the hind-limbs alone are 

 visible, I find three nephrostomes in the head-kidney, the cells of 

 which bear long flagella pointing inwards, as Hoffmann has 

 pointed out. The first of these is situated some way in front of 

 the glomerulus, the second immediately in front of the attachment 

 of the glomerulus, and the third immediately behind it. 



In my next stage ; that is to say in a frog 38 mm. long (in- 

 cluding the tail, which was about 21 mm. long), one nephrostome 

 only remains ; but, as this is situated some considerable distance 

 in front of the glomerulus, it must be regarded as the first and not 

 the third of the preceding stage. Immediately ventral to it 

 there is a groove in the peritoneum, open below, the epithelial 

 lining of which is very columnar and quite different in appearance 

 to that of the nephrostome. This columnar epithelium is con- 



13—2 



