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

DEVELOPMENT OF AMPHIBIAN KIDNEY 453
into the main mass of the kidney where it splits, in the ordinary
manner, into numerous branches to the glomeruli of secondary
malpighian capsules, and to the excretory portions of the
secondary tubules.
These accessory funnels increase their number by direct
splitting from the end of the tail to the funnel, as is seen in
fig. 15, PI. 22. It will be noticed also that the renal arterioles
(r.at.) are similarly doubled, one branch being associated with each
tail of the funnel. Only one of these tails is cut, and is seen lying
just above the larger artery; the other runs directly away from,
and in a plane at right angles to, the observer.
It is fairly universally accepted that the function of the
glomerulus is confined to the adjustment of the water content
of the blood and that the excretion of nitrogenous waste takes
place through the renal tubules. It seems, therefore, very
probable that the tails of these accessory funnels may have an
excretory function, the waste products being passed to the
arterioles. If this is not so, there is no apparent reason for the
existence either of the tail, or of the special arteriole: if this
postulate be accepted, then the production, function, and
correlation of the whole series of peritoneal funnels becomes
clearer.
In Text-fig. 2 are shown two stages in the production of
a peritoneal funnel by each of the methods described. In A and
B the funnel, closely associated with, but not opening into, the
malpighian unit, directly connects the coelomic cavity with a
venule. The artery supplies both the water-adjusting glomerulus
and the waste-excreting tubule. This method is found only
in young tadpoles and is a relic, of phylogenetic interest, of the
urodele type. In E, which begins a few weeks before, and
continues for a few months after, the tadpole leaves the
water, special tubules connect the dorsal blastema mass to the
peritoneum. In C and D, which begins during the first and
continues during the second and third years spent by the frog
on land, the blastema has shifted to the peritoneal surface and
the tubules have acquired a tail with an arterial supply.
These observed facts of structure can be exactly correlated
with the observed habits. As a tadpole the larva is not subject