Flew). — Pronephros hi Amphibia. 



PLATE IV. 



Fig. 28. Part of a cross section through the anterior trunk region of a larva 

 belonging to Stage VI. The Figure shows the pronephros in the 

 region of the first nephrostome. X 110. 



Fig. 29. Part of an oblique longitudinal section through a larva of Stage IV. The 

 plane of the section was directed so as to cut the somatopleure tan- 

 gentially along the line of the three nephrostomes. Its direction is 

 represented by the line 40 in Figure 20. X 110. 



Fig. 30. Part of a cross section through the middle trunk region of a larva, 

 from which Figure 28 was also drawn. (Stage VI.) X 110. 



Fig. 31-38. A series of diagrams illustrating the convolution of the pronephric 

 tubules. These diagrams, which are based upon reconstructions 

 from cross sections, merely serve to show the number and approxi- 

 mate location of the loops in a longitudinal direction. No attempt 

 has been made to indicate in the diagrams the changes in position 

 undergone by the tubules in a transverse direction. The gray tint 

 represents the common trunk and the anterior portion of the seg- 

 mental duct. The first nephrostomal tubule and the collecting 

 trunk are colored pink. The second and third tubules are repre- 

 sented in yellow and orange respectively. 



Figs. 31-34 are from various larvae of Stage V. 



Fig. 32 is a diagram of the reconstruction shown in Figure 40. 



Figs 33 and 34 represent the right and the left pronephros respectively of the same 

 individual. 



Figs. 35-37 are from various larvae of Stage VI. 



Fig. 36 is a diagram of the reconstruction shown in Figure 41. 



Fig. 38 is from a larva of Rana halesina. 



Figs. 39-41. A series of reconstructions from cross sections of larvae in different 

 stages of development. In Figures 40 and 41, the common trunk 

 and the anterior portion of the segmental duct have been shaded 

 without color ; the collecting trunk and the first nephrostomal 

 tubule have been colored pink ; and the second and third nephro- 

 stomal tubules are respectively yellow and orange. X 65. 



Fig. 39. Right pronephric pouch of a larva belonging to Stage IV., viewed from 

 the median side. The X's represent the position of the nephro- 

 stomes. The lines 18-21 show the various levels at which the sec- 

 tions represented in Figures 18-21 were made. 



Fig. 40. Right pronephros of a larva belonging to Stage V., viewed from the 

 median side. 



Fig. 41. Right pronephros of a larva belonging to Stage VI., viewed from the 

 ventral side, the external face being uppermost. 



