Field. — Pronephros iu Amphibia. 



PLATE III. 



Figures 18-22 and 27 are magnified 110 diameters; Figures 23-26, 260 



diameters. 



Figs. 18-22 Portions of a series of cross sections through an embryo of Stage IV. 

 In Figure 18, the pronephros of the right side is shown ; in the 

 remaining Figures, the pronephric organs of the left side. The 

 location of the several sections on the reconstruction (Fig. 30) is 

 shown by the series of lines bearing corresponding numbers. 



Fig. 18 shows the first nephrostome. 



Fig. l'J is from a region between the first and the second nephrostomes. 



Fig. 20 shows the second nephrostome. 



Fig. 21 shows the third nephrostome and the anterior portion of the segmental 

 duct. 



Fig. 22 shows the segmental duct in the middle trunk region. 



Figs. 23-26. Cross sections of the fundament of the segmental duct near its pos- 

 terior termination, from an embryo of Stage IV. 



Fig. 23 shows the duct five sections in front of its termination. 



Fig. 24, three sections before its termination ; a., b., and c, cells in the fundament 

 of the duct ; <d., portions of the two cells c. and </., which are to be 

 seen in the following section. 



Fig. 25 shows the duct one section in front of its termination ; c. and (/., cells in the 

 rudiment of the duct ; b. and c, portions of two cells bearing the same 

 lettering in Figure 24. 



Fig. 26 shows the depression of the somatopleure (/. ) directly behind the tip of the 

 fundament of the duct. 



Fig. 27. A cross section from a larva whose pronephros is shown in Figure 41. 

 It shows the opening of the segmental duct into the cloaca. 



