THE DEVELOPMENT OF THE MULLERIAN DUCTS OF REPTILES. 617 



section of the same series. In it the thickened plate is seen yet further forward in the 

 lateral diverticulum of the ccelom. Figs. 9 and 10, which represent still more ventral 

 sections, show the ventral extension of the plate : in the former, the thickening appears 

 still dorsal and internal, but projecting towards the lateral wall of the ccelom ; in the 

 latter, the seventy-fourth section more ventral than fig. 9, the end of the ventral 

 extension of the anterior plate is seen raised on a more prominent ridge, just anterior 

 to the liver. 



My third stage (C), found in a specimen of probably less than 20 mm. in length, 

 shows a modification of the anterior thickened epithelial plate, that is interesting as 

 being similar to what is found in amphibia (6). The plate is undermined by a diver- 

 ticulum of the ccelom ; and by the splitting of the plate the foundation is partly 

 divided into two areas, the one of which is connected with the ventral extension of the 

 plate, while the other leads directly back to the Mullerian duct. 



The pronephros of C has degenerated completely, but along the anterior ccelomic 

 diverticulum there is still a distinct band of thickened epithelium. This spreads out to 

 form a broad plate in the region just in front of the mesonephros. Under this plate a 

 slight diverticulum of the ccelom is seen (d., fig. 11), and examination of the posterior 

 margin of the plate reveals the fact that the plate has been partially divided by the 

 breaking down of the slight partition between the old diverticulum and the new one. 

 The inner end of the plate remains projecting laterally between the united diverticula, 

 while the outer end projects slightly from the lateral wall (r., fig. 11). From the fact 

 that the external remnant of the plate continues to extend into the body-cavity through 

 a considerable number of sections, it is evident that the anterior plate formerly extended 

 much further. 



My next specimen (D) is 19 mm. in length, and illustrates even better than the 

 last one the division of the anterior foundation. 



The anterior diverticula expand posteriorly, and along the lateral epithelium, but 

 nearly dorsal, there appears a distinct narrow band of thickened epithelium. Where 

 the glomus first appears, projecting slightly forwards into the diverticula, the ridge 

 spreads out to form a plate, and at the same time the diverticula open into the main 

 division of the ccelom. The anterior part of the plate has apparently been largely 

 obliterated by the secondary attachment of the radix mesenterii to the lateral body-wall. 

 The plate is at this stage divided at the anterior end of the mesonephros, and, as in C, 

 the two posterior (ventral and dorsal) continuations of the thickened plate pass back, 

 separated by a deep channel. The dorsal division hangs free into the ccelom, which has 

 undermined it from its ventral edge ; and it only gradually passes into connection with 

 the mesonephros. The ventral division is found to pass the base of the lung, and ends 

 just anterior to the beginning of the liver. 



I have examined specimens up to 75 mm. in length, and all of them show similar 

 relations of parts. In all, there is the anterior lateral plate. It is usually slightly 

 undermined, and is divided posteriorly to form two bands, one of which leads to the 



