ment of the Kidney, and the Development of the - Journal of Cell ...

DEVELOPMENT OF AMPHIBIAN KIDNEY 461
It is apparent that all these irregular coils and lumps have
little relation to a normal kidney unit, the functions of which
they most certainly cannot carry out, and that the anterior
prolongation, though its structure and affinities suggest a vas
efferens, will never carry sperm. It is a well-known fact that
kidney blastema cells, when cultured in vitro with connective
tissue cells, form well-differentiated tubules. This anterior
region represents a culture, not in vitro but in vivo. The
straight tubules, which are found very early in development,
are formed fairly normally, but the remaining blastema, left in
an area which has no sexual or excretory use, merely forms
tubules in an aimless manner.
From these reconstructions, however, there emerge the facts
that, during the second year after metamorphosis:'
(1) The vasa efferentia run from the kidney to the edge of
the testis.
(2) Within the kidney the vasa efferentia end in a mass
of blastema representing Bidder's canal which is itself
directly attached to an abortive unit terminating a straight
tubule.
(3) The sperm-collecting network within the kidney is not
yet connected to the vasa efferentia but is connected to an
anterior prolongation which runs through the fat-bodies to end
in a remarkable mass of tubules at the extreme anterior end of
the kidney.
We already know, however, from an examination of a 22-mm.
stage that:
(4) The edge of the testis is connected to the kidney from the
earliest stage where either is recognizable.
There remains only to trace the origin and fate of the anterior
prolongation and the manner in which the solid kidney-testis
connexion becomes broken up into vasa efferentia.
The sheet of blastema which, in the 22-mm. tadpole (fig. 20,
PI. 22), connects the gonad to the kidney lies on the surface of
the inter-renal vein. This vein increases very rapidly both in
size and length; the blastema cells do not increase in number.
The natural result is that the sheet of tissue is broken into a
number of irregular masses. It is common knowledge that the