REMOVAL OF PRONEPHROS OF AMBLYSTOMA 369 
were immersed in 0.4 per cent NaCl in an attempt to balance the 
loss of essential salts through the escape of the glomerular 
filtrate. Although shghtly stimulated heart action resulted, 
probably due both to the stimulus of operation and to relieved 
pressure in the pericardial cavity, only temporary benefit was 
derived in this way, for, with the accumulation of new fluid, the 
former pathologic condition was restored, and death followed 
after a short interval. It is quite possible that if a sufficient 
number of experiments were made, varying the constituents of 
the solution in which these larvae were kept, a satisfactory 
medium might be found for prolonging the life of these animals. 
A determination of the optimum salt percentages of such a solu- 
tion has not yet been undertaken. 
The second means employed was the transplantation of the 
pronephric rudiment to the region of the mesonephros. It was 
by this means possible to test the capacity for reestabhshment 
of function, through union with the segmental duct. In a series 
of thirty embryos, the right head kidney, without the ectodermal 
covering, was placed under the skin farther back on the same 
side. Twenty-four hours later, the left pronephros was removed 
from those embryos which had responded well to the first opera- 
tion and were apparently recovered. The transference and 
proper orientation of the kidney in these operations was easily 
accomplished and the wounds healed entkely in the usual short 
time, but the general edematous condition common to embryos 
on which only the bilateral excision had been performed sub- 
sequently developed. With the exception of a few which were 
preserved and sectioned at the end of a week, all of this series 
died within twelve days, showing no indication of resumption of 
function by the transplanted tubule. The transplanted tubule 
still retained its identity, although as a general rule the cells 
were pressed together in a solid mass, and only in a few instances 
a distinct lumen was visible. Removal of the pronephros 
resulted here in the partial or total atrophy of the segmental duct, 
to which attention will be called in greater detail below. How- 
ever, in cases where the transplanted tubule had been placed in 
the immediate region of the segmental duct, no connection was. 
