366 RUTH B. ROWLAND 
Larvae in which the triple-incision method was used healed 
much more slowly than those to which the second method was 
applied, since contraction of the cut edges left a gaping wound 
much greater in extent and permitted more oozing of the yolk. 
On the other hand, when only one cut was made, a critical 
inspection of the excised tubules was necessary to make sure of 
total removal. In the majority of cases the incision is entirely 
healed at the end of an hour and a half. 
Effect of bilateral removal 
Most conspicuous of any of the postoperative conditions 
resulting from bilateral excisions was a pronounced edema, par- 
ticularly in the anteroventral region. It is well known that 
edema of the amphibian embryo commonly occurs as the result 
of a variety of causes. Narcotized embryos reared in a solution 
of acetone-chloroform (chloretone) , though structurally normal 
in other particulars, show a slight edema and pericardial effusion 
as a result of weakened heart action (Harrison, '04). More 
pronounced abnormahties result when early developmental 
stages are exposed to the heat of direct sunhght, or may be 
induced experimentally by exposing the embryos to radium 
rays (O. Hertwig, '11). McClure ('19), in his recent work on 
edema in anuran larvae, draws attention to the ''less extensive 
tubular complex which normally occupies a dorsolateral position 
in the pronephros, and into which the nephrostomal canals 
directly open," and the "tubules which normally constitute the 
greater portion of the kidney and which occupy a medial and 
ventral position." From a study of the histological conditions 
existing in edematous frog larvae, he concludes that there is a 
functional as well as a morphological difference between these 
two regions, for in all of the embryos in which edema had become 
apparent, the ventrolateral tubules were either entirely absent 
or but poorly developed. From this he argues that deficiency 
in the ventrolateral tubules alone may be the cause of edematous 
conditions. 
