:r22 MR GREGG WILSON ON THE DEVELOPMENT 



plate, there persisted a thick band running down the middle diverticulum, and passing 

 obliquely towards the middle line before narrowing to a thread, and accompanying the 

 segmental duct (see p. 515). That stage was found in a specimen 37 mm. long ; my 

 next size is 40 mm. in length ; but as a specimen 46 mm. long represents an intermediate 

 stage in the development of the Miillerian duct, I shall describe it first. 



This Salamander has no longer any appearance of a pronephros, but the glomerulus 

 persists. Opposite the anterior end of the glomerulus there is a narrow lateral band of 

 heightened epithelium, representing the anterior end of the Anlage of the Miillerian 

 duct. After fourteen sections the band broadens into a plate and becomes dorsal in 

 position — just opposite the posterior end of the glomerulus. After other fourteen sections 

 the plate covers the whole dorsal aspect, and a diverticulum of the ccelom makes its 

 appearance underneath it. Eight sections are undermined before the lateral margin of 

 the plate loses its connection with the body- wall, just as was described in the case of 

 Axolotl. For about a dozen sections after the breach, the plate continues to project 

 laterally into the coelom. At this stage a groove appears in the top of the now 

 narrowed plate ; but there is no appearance of inclosing, and the ridge gradually passes 

 into a low backward running band. The segmental duct is not visible ; and there is 

 only the change of direction, from oblique to antero-posterior, to give any indication of 

 where the " anterior mode of formation " probably ends. 



In a Salamandra atra of 40 mm. (G) a further stage in the development is shown. 

 There is no longer any appearance of either pronephros or glomerulus. The anterior 

 of the Miillerian duct is again met with on the lateral wall, lying well to the outside of 

 the lung. After the first few sections its inner margin exhibits a curious pointed 

 projection, which at once recalls the remnant already described as left on the lateral 

 wall (in the case of both Axolotl and the last specimen of Salamandra atra referred to) 

 when the epithelial plate is ruptured. But here there is no sign of thickened epithelium 

 opposite the projecting side-piece. After about thirty sections, when this projection has 

 disappeared, and the band has become dorsal instead of lateral, the Anlage begins to 

 rise on a ridge which projects outwards from the middle line, and through many sections 

 shows its origin by splitting from the lateral wall. After other twenty sections a slight 

 groove appears ; and as the posterior is approached the furrow becomes deeper and 

 deeper, and finally closes some thirty sections after the beginning of the groove. The 

 other side of this form is similar to the one described, but the anterior ungrooved region 

 of the epithelium is much shorter, and the inclosing is much further forward. 



The explanation of the appearances just described is got from one of my 46 mm. 

 specimens (H). In it, too, the anterior of the Miillerian duct is found projecting 

 inwards, while further back the direction is outwards; here, again, there is an 

 intermediate flat band. The difference is, that in this case the furthest forward part 

 of the duct is not quite so far on in its development as in G, and the actual occurrence 

 of a separation of the Anlage from the inner (more dorsal) wall of the coelomic 

 diverticulum. So far as the epithelial plate is dorsal, the separation is from the outer 



