hall: mesonephros and mulleeian duct in amphibia. 85 



Larva X, 53 mm. — Gills reduced to stumps. 



Oil the right side of this larva the anterior evagiiiation has almost 

 totally disappeared, as well as that part of its duct which was anterior to 

 the second evagination (Fig. i\^, p. 88). The duct from the second evagi- 

 nation divides, however, almost immediately into an open tube and an 

 irregular cord. These soon reunite to form one large duct with two 

 lumina, which finally merge into a single lumen. The condition of the 

 distal (caudal) end of this duct I shall describe presently. On tlie left 

 side of the body both evaginations are still present with their ducts, 

 which at first are widely separated, then approach and have a common 

 sheath. They do not unite completely until they reach the region of 

 the fiftieth section back of the second evagination. The resultant duct 

 fuses with the Wolffian duct. The second evagination is so far back 

 that it lies in the ridge whose formation was traced in Larva IX. This 

 causes the thickened band and the duct from the second evagination to 

 form an almost straight line, as shown in Figure iV. 



The distal end of the Miillerian duct on the right side of the body 

 presents as strong evidence as any I possess, that a portion of the Miil- 

 lerian duct may fuse intimately with, and possibly take cells from, the 

 Wolffian duct. As the question of the participation of the Wolffian 

 duct in the formation of the Miillerian duct has been so much discussed 

 and is of such great theoretical interest, it seemed best to make draw- 

 ings of a number of consecutive sections and thus give the reader a better 

 opportunity to judge for himself as to the evidence. 



As was previously stated, the single duct, formed by the fusion of 

 those from the two evaginations, runs for a certain distance close to 

 the Wolffian duct, but enclosed in its own sheath ; that is, a layer of con- 

 nective tissue separates it from the Wolffian duct. Back of this the duct 

 approaches the Wolffian duct and this connective-tissue layer is in- 

 terrupted, thus allowing the Miillerian duct to apply itself to the 

 Wolffian. Figures 54 to 63 (Plate 5) show ten consecutive sections 

 immediately posterior to the point where this juxtaposition takes place. 



In Figure 54 is seen a mass of tissue extending from the Miillerian 

 duct (which a few sections farther forward is quite free and in cross- 

 section regularly rounded) to apply itself to the Wolffian duct. The two 

 following sections (Figs. 55 and 56) show the Wolffian duct distorted 

 in such a w^ay that its median wall is continuous with this mass of cells. 

 In Figure 57 the mass is quite distinct from both ducts, and the Wolffian 

 duct has regained, to a large extent, its typical shape. In Figures 58 



