509 



pr. d. 



ncp. 



differentiated posteriorly, accounts for the apparent origin of the 

 posterior mesonephric tubules from coeloniic epithelium and the origin 

 of tlie anterior tubu- 

 les from the mesoderm 

 dorsal to the coelomic 

 epithelium. 



As in the kidney 

 development of other 

 animals I noticed that 

 the mesonephros deve- 

 lops from before back- 

 wards, any one indi- 

 vidual embryo thus ex- 

 hibiting many different p''- '^■ 

 stages. Thus in passing 

 from the front end of 

 the mesonephros cau- 

 dalwards the first meso- 

 nephric tubules resemb- 

 led the posterior pro- 

 nephric tubules and a 

 gradational change was 

 observable. 



The more impor- 

 tant points in the early 



development of the kid- pig. XIII. Transverse section of a Scyllium canicula 



ney in Chrysemys may e'^ibryo (7 m.m. long). The section is the fifth behind 



, , . „, . , that represented in Fig.XII and passes through somite IX. 



be briefly summarised Lettering as in Fig. XL 



as follows: — 



(1) The pronephric tubules arise from the somatic layer of the 

 nephro tome, from a primitively continuous "Anlage". 



(2) The origin of mesonephric tubules is twofold: — the portion 

 nearest the segmental duct arises from the somatic layer 

 of the nephrotome and the other portion from the coelomic 

 end of the nephrotome. 



(3) The glomus is formed between the aorta and pronephric 

 tubule openings, the glomeruli have a covering originating 

 from the splanchnic wall of the nephrotome. 



