10 W. F. K. WELDON. 



A section through the next protovertebra would repeat the 

 features shown in fig. 24. 



On the appearance of the fifteenth protovertebra the lumen 

 of the Wolffian duct becomes continuous throughout the region 

 of the first eight segments, and at the same time it acquires a 

 communication with the cavity of each segmental vesicle in its 

 course. 



The first eight segmental tubules are therefore differentiated, 

 continuously with the Wolflian duct, from a ridge of cells, con- 

 tinuous at first along its entire length with the peritoneal 

 epithelium, and at certain points with the adjacent proto- 

 vertebrae. 



With regard to the tubules behind the eighth, they are 

 developed from the intermediate cell mass in exactly the same 

 way as those in front ; but the Wolffian duct, instead of arising 

 continuously with them, grows backwards as a free projection 

 of the above-described portion, without coming into relation 

 with adjacent structures. It is at first solid, but afterwards 

 acquires a lumen, and becomes connected with the segmental 

 vesicles in order from before backwards. 



On the subsequent behaviour of the tubules and on the 

 development of the metanephros I have no observations. 



The most interesting feature in the preceding account of the 

 early development of the lacertilian kidney is the close resem- 

 blance which it shows to exist between the process of develop- 

 ment in that group and the process which has been shown by 

 Sedgwicki jq exist in birds and Elasmobvanchs. In both these 

 groups Sedgwick has shown that the segmental tubules arise 

 from a continuous cell mass connected with the peritoneal epi- 

 thelium and with the mesoblastic somites, which cell mass is 

 present from the very beginning of the process of mesoblastic 

 segmentation. 



In the anterior part of the Wolffian body of the chick 



1 Sedgwick, " Development of the Kidney in its relation to the Wolffian 

 Body in the Chick," this Journal, vol. xx; and "Early Development of the 

 WolDBan Duct and anterior Wolffian Tubules in the Chick," &c., 'Quart. 

 Journ. Mic. Sci.,' vol. xxi. 



