232 
ZOOLOGY: R. B. ROWLAND 
muscles began, for contraction not only hindered the operation, but 
often tore open the wound after successful removal of the kidney. 
Two methods were employed in removing the pronephroi. In the 
first, three straight cuts were made, one beneath and one along each side 
of the pronephric prominence. The flat of skin thus defined was Ufted 
up and the organ removed from below. In the second and more satis- 
factory method, a single incision was made dorsal to or iromediately 
over the thickening, the needle inserted, and the tubuje raised upward 
from the ventral side and excised. 
Conditions ensuing upon the removal of the head kidney of both sides 
in Amblystoma larvae show clearly that these organs are necessary to the 
life of the embryo, although the presence of one pronephros suffices to 
keep the organism alive and in a healthy condition. All embryos from 
which both head kidneys had been excised died within eight to twelve 
^ days, evidencing during 
^VV''*"^^^^^ that interval symptoms 
of weakened heart- 
action — oedema and ef- 
fusion into the peri- 
cardial and abdominal 
cavities — presumably 
brought about by ure- 
mic poisoning. Prick- 
ing the body wall to 
relieve the dropsical condition was resorted to in many cases from five 
to seven days after operating, but it proved ineffective. 
The pronephros remaining after the removal of one head kidney evi- 
dently takes over the function of excretion usually performed by the 
two organs, and, concomitant with the increased physiological activity, 
presents marked morphological changes. The size of the organ which 
functions alone is greatly increased, indicating the occurrence of com- 
pensatory hypertrophy. In the normal pronephros, the walls of the 
tubules are thick, and consist of cuboidal cells, the central ends of which 
often bulge out into the narrow lumen. The hypertrophied tubules are 
thin walled, the cells flattened as is the case in normal larvae of greater 
age, and the lumen accordingly is nearly twice that of the unoperated 
specimen. To determine the nature and extent of the change brought 
about in the functioning pronephros through the removal of the organ 
on one side, wax models of this organ (X 200) of an operated specimen 
and of a normal embryo were constructed. The control was chosen 
from a large number of normal embryos which, on sectioning, showed 
FIG. 1.— AMBLYSTOMA EMBRYO IN THE OPERATING 
STAGE, SHOWING THE PRONEPHROS EXPOSED AFTER RE- 
MOVAL OF ECTODERM. X 13. 
