360 RUTH B. HOWLAND 
phibian kidney, although Levi ('05) claims that the anuran 
mesonephros has, in one species, the power of regeneration after 
injury. He destroyed both the urogenital anlage and that 
of the wolffian duct and tubules in Bufo larvae by means of a 
red-hot needle, and obtained after a certain time complete 
regeneration of the excretory organs. His method is, however, 
open to the criticism that no accurate estimate of the actual 
extent of the injury done to the organs by this type of operation 
can be made. The introduction of a hot needle may cause only 
minor displacement or destruction of a few cells of the duct or 
coils. Certainty as to the degree of injury can be assured 
only by complete excision. 
Removal of a portion of a given organ or system has been 
found to have a varied effect on the formation of its other constit- 
uents. The extent to which the growth of one part is influenced 
during its development by other developing portions of the 
embryo varies widely, the scale of difference ranging from com- 
plete interdependence to those extremes in which each con- 
stituent possesses the potency for self-differentiation without 
the influence of any formative stimuli. 
In view of this variation in the degree of correlation exhibited 
by closely related parts during their early growth, it was of interest 
to consider, particularly in cases of bilateral extirpation of the 
pronephros, the effect of the absence of the tubules on the forma- 
tion of the glomeruli. The operated animals showed without 
exception a differentiation of glomerular tissue perfectly normal 
in position and size. The glomerulus therefore possesses the 
power of self-differentiation, and is entirely independent of the 
presence of the tubular elements. 
It gives me great pleasure to acknowledge my indebtedness to 
Prof. R. G. Harrison, at whose suggestion this investigation was 
begun, for his helpful and constructive criticism during the 
course of my work. 
