OF THE MULLERIAN DUCT OF AMPHIBIANS. 513 



each side there is a diverticulum (d 1 ) which has been cut off by an outgrowth of the 

 radix mesenterii ; next come two middle diverticula (d 2 ) formed by the fusion of the 

 lungs with the lateral walls ; and the remainder of the ccelom, ventral to the gut and 

 lungs, forms the fifth division (c). 



Where the pronephros begins the ccelom is simple at this stage of development, 

 though at later stages the epithelium on the pronephros is found to be divided by the 

 backward growth of the radix mesenterii and the connection of the lung with the 

 body-wall. 



Anterior to the first nephrostome, the pronephros is remote from the median line 

 of the body- cavity, lying as far lateral as possible. Further back, the pronephros is 

 dorsal as well as lateral, and the second nephrostome opens mucli nearer the middle 

 line than the first. 



The glomerulus of the pronephros appears exactly opposite the posterior of the 

 first nephrostome, and extends back through twelve sections, two-thirds of the distance 

 between the two nephrostomes. In several sections towards its posterior end it appears 

 (on both sides) fused with the peritoneal epithelium on the pronephros. 



The ordinary epithelium on the pronephros is low, plate-like, and inconspicuous ; 

 the nephrostomes, on the other hand, are lined with distinct flagellate cells of cylindric 

 form, which pass into an epithelium whose cells are brick-shaped ; while this, in turn, 

 gives place somewhat suddenly to the ordinary peritoneal epithelium. There is thus a 

 ■plate of heightened cells round each of the nephrostomes ; and I regard this fact as of 

 considerable interest, inasmuch as in later stages the isolated patches of heightened 

 epithelium unite and give rise to one plate of considerable dimensions, from which, as 

 1 shall show, the anterior of the Miillerian duct is formed. 



Posterior to the pronephros the segmental duct, after passing nearer to the middle 

 line and turning in a spiral, goes backwards in a straight line to the mesonephros. It 

 is worthy of note that this spiral in the course of the segmental duct occurs just where 

 Hoffman has described a splitting of the duct to form Miillerian and Wolffian ducts. 

 The appearance of single sections might well lead to the supposition that there was 

 splitting or budding (figs. 2, 3, and 4), where examination of a series reveals only 

 change of position of the duct, 



In another specimen (B) 13 mm. in length, the relations of parts are somewhat 

 different. At the level of the beginning of the pronephros the alimentary canal 

 is now united with the dorsal wall of the ccelom over its whole surface, and the 

 ccelom is divided into three distinct regions by the fusion of the lungs with the lateral 

 walls. Five sections further back (in the sixth section anterior to the first nephro- 

 stome), the five-fold division of the body-cavity is met with ; and in this specimen is 

 still found at the level of the first nephrostome (fig. 5). 



In this case, therefore, the first nephrostome opens not into the simple ccelom, but 

 into a diverticulum of it (d 1 fig. 5) that is inclosed by the secondary attachment 

 of the alimentary canal. The heightened epithelium in the neighbourhood of the first 



