THE DEVELOPMENT OF THE MULLERIAISr DUCTS OF REPTILES. 615 



The Mullerlan Ducts of the Crocodile. 



I shall now describe the various stages examined by me in Crocodilus biporcatus. 



The first of these (A) is found in a specimen of 10 mm. in extreme length. In this 

 the ccelom is simple in the region of the pronephros.* There are, however, lateral 

 ridges along the alimentary canal, indicating the line of the usual secondary connec- 

 tion with the somatopleure (fig. 1, l.r.). These ridges gradually become lower as we 

 follow them towards the posterior end, and finally are lost in the mesentery. 



The first section through the pronephros shows a nephrostome, one tubule, and the 

 anterior end of the glomus. The nephrostome has already lost connection with the prone- 

 phros, so that the funnel is quite isolated ; while, posterior to the nephrostome, the 

 pronephros has degenerated so far that through several sections it ceases to appear. It 

 is noteworthy, however, that the heightened epithelium of the nephrostome extends out 

 on all sides, and passes back towards the posterior end as a distinct thickened band. 

 This unites the anterior nephrostomes, and passes gradually into the ordinary epithelium 

 of the ccelom. 



The next stage that I have is got in a specimen (B) 12 mm. long. Anterior to the 

 excretory organ and the glomus, we see in transverse section three divisions of the 

 ccelom ; and in the dorsal diverticula formed by secondary fusion of the alimentary canal 

 with the body-wall, we find again distinct thickenings of the epithelium. These, at first, 

 are ventral in position (fig. 2, m.d.) ; but, anterior to the beginning of the glomus, they 

 lie on the lateral and dorsal walls of the diverticula (fig. 3). The lateral anterior part of 

 the embryonic excretory organ found in A has disappeared, and with it its nephrostomes ; 

 but a few sections further back than the anterior of the glomus, the remainder of the 

 embryonic excretory organ is met with, and just external to this the above-mentioned 

 thickening runs along the lateral wall of the ccelom. It is not, however, only on the 

 lateral wall immediately external to the pronephros that the thickening is found passing 

 back, for, opposite the anterior end of the mesonephros, the thickening, which is at first 

 simple, passes back as two distinct bands, one of which lies close to the mesonephros, 

 while the other is quite ventral to the diverticulum (fig. 4). The lateral wall shows an 

 intermediate area of ordinary ccelomic epithelium. A little further back, where the 

 dorsal diverticulum opens into the ccelom proper, the ventral thickening is altogether 

 separated from the dorsal one (fig. 5). It gradually becomes less conspicuous, and 

 passes into the ordinary epithelium of the ccelom. 



The occurrence of this band recalls the ventral extension of the Mullerian ducts in 

 elasmobranchs, and the temporary ventral growth of the Mullerian duct foundation in 

 Rana. 



The more dorsal backward prolongation of the lateral plate narrows gradually as it 

 passes back. It comes to lie on a bridge of tissue that is between the cardinal vein and 

 the mesonephros ; and at the same time it becomes grooved. External to the thickening, 



* Identified by Wiedersheim. 



