REMOVAL OF PRONEPHROS OF AMBLYSTOMA 365 
Parallel with this development, although not appearing at so 
early a stage, the rudiment of the glomerulus is formed. This 
first appears as a thickening in the opposite or splanchnic wall 
of the coelom, extending over an area as long as the distance 
between the anterior and posterior funnels. Vascular cavities 
soon appear, and at an early stage these become continuous 
with branches of the dorsal aorta. The arterial supply is derived 
directly from this source; the venous supply from the postcar- 
dinal vein, which enlarges in the region of the pronephros, form- 
ing a large venous sinus, into which the fully developed kidne}^ 
projects. The tubules are thus continually bathed in the blood 
returning from the posterior part of the body (Field, '91). 
BILATERAL EXCISION OF PRONEPHRIC RUDIMENTS 
Mode of operation 
The first experiments consisted in the removal of the proneph- 
ric rudiments on both sides, to test the functional necessity of 
these primary organs in the life of the embryo. 
In the largest proportion of cases, a period of several hours, or 
even a day, was allowed to elapse between the removal of the 
right and left pronephros. However, the two excisions may 
follow each other immediately without incurring serious results. 
Sharp-pointed needles, inserted in glass rods, were substituted 
for the more generally used iridectomy scissors. Controls were 
kept under identical conditions of light, temperature, water, 
etc. Two methods were employed in removing the pronephros. 
In the first, three straight cuts were made, one beneath and one 
along each side of the pronephric swelling. The flap of ecto- 
derm thus defined was loosened from the underlying mesoderm, 
and the organ removed from below. In the second and more 
satisfactory method, a single incision was made, dorsal to or 
immediately over the thickening, the tubule raised upw^ard from 
below, pulled outward, and excised. In loosening the nephros- 
tomal surfaces of the funnels, as much of the tissue in a dorso- 
median direction was removed as seemed possible without 
disturbing the splanchnopleuric wall, since in this region the 
glomerulus normally arises. 
