REMOVAL OF PRONEPHROS OF AMBLYSTOMA 
375 
was 78 mm. (0.13 mm. in actual size), as contrasted with 130 
mm. (0.216 mm. in actual size) for PN 7 — a fact suggesting the 
large percentage of increase in functional capacity of the two 
kidneys determined and described below. From these projec- 
tions also the thickness of the walls was estimated by taking the 
average of sixty measurements in each kidney. The average 
thickness of the wall of the normal kidney is 10.9 mm. at a mag- 
Fig. 11, PN 7 d Normal tubules with thick walls, and cells bulging into the 
lumen. X 240. 
Fig. 12, PN 7 Hypertrophied tubules with large lumens and thinner walls. 
X 240. 
nification of 600, or 0.0181 mm. in actual measurement. For 
the hypertrophied kidney, the average thickness is 7.8 mm. at 
a magnification of 600, or 0.013 mm. in actual measurement. 
Having the length of the two kidneys, determined from the 
models, and considering each kidney as a simple cylinder, with 
the average measurement just obtained as its circumference 
and the length as its height, the areas of the inner surfaces in 
each were computed. In the normal kidnej^ the area of the 
secreting surface was found to be 1.007 sq. mm. as contrasted 
