501 



with Telleyesniczky's Bichromate-acetic and the older ones in 

 Zenker's fluid, I stained these in bulk with Grenachee's borax- 

 carmine and Ehrlich's Haematoxylin respectively. As these embryos 

 ranged from the time of the appearance of the primitive streak on- 

 wards by successive slight differences in age I was enabled to make 

 a comparison of the kidney in embryos at many different stages. 



In addition to a description of the pronephros and its duct, the 

 mesonephros, glomus and glomeruH, I hope to add observations upon 

 the development of the metanephros and its duct and the Miillerian 

 duct in Chelonia, and upon the " epididymis " of the adult male. 



Description. 

 In a Chrysemys marginata embryo with 11 protovertebrae, traces 

 of the kidney are visible in the region extending from segments YII 

 to X (inclusive) : the " Anlage " is in the form of a continuous groove 

 or thickening of the somatic layer of the nephrotome, immediately 

 beneath the somite (see Figs. I and II). 



/. am. t. am. sp. cd. ntcd. som. ect. an.pr. d. som. I. p. 



end. spl. I. p. 



Fig. I, Transverse section of a Chrysemys embryo 'with 11 protovertebrae. 

 On the left of the figure segment VI on the animal's right side is cut through about 

 the middle ; on the right side of the figure the front end of segment VII on the 

 animal's left side is cut through. 



an.pr. d. "Anlage" of pronephric duct; ec^ ectoderm ; end. endoderm; f. am. 

 false amnion ; ntcd. notochord ; som. somite ; som. I. p. somatic layer of lateral plate ; 

 sp. cd. spinal cord ; spl. I, p. splanchnic layer of lateral plate ; t. am. true amnion. 



At this stage the process of segmentation has affected the meso- 

 derm situated on either side of the notochord (mesodermic somite), 

 but has not yet affected the mesoderm of the nephrotome : hence the 

 distal portion of the above-mentioned thickening— which will become 

 the pronephric duct— is from the first a continuous structure. 



