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

DEVELOPMENT OF AMPHIBIAN KIDNEY 459
excretory unit joins the straight tubule at ae. and the malpighian
capsule (me.) of this unit appears lower in the figure. The vas
efferens (ve.) is not directly attached to the unit but terminates
in the rudiment of Bidder's canal (rb.). It will be realized that
the interconnexions of all these parts are rather complex and
best studied in a reconstruction.
Fig. 9a (PI. 21) shows a reconstruction of this same region;
at 9 b the reconstruction has been dissected. The straight tubule
(st.) passes under the malpighian capsule (me), curves upwards
towards the observer, and then passes to the right before looping
across, down, and back to the malpighian capsule. There is no
trace of any of the conventional tubule divisions of a normal
unit. From the base of the loop indicated by z in fig. 9 b, PI. 21,
a solid strand of cells leaves the inner side of the middle loop.
This passes out through the middle of the loop to the right and
turns back (ca.) to become attached (at ax., seen in both 9 a
and b) to an irregularly ovoid mass of blastema (rb.). A thick,
irregular projection from the upper side of this mass of blastema
curves upwards and over to narrow down as the vas efferens
(ve.). It is obvious that both ca. and ve., though they are distinct
at this point, contribute to the adult vas efferens; and that rb.
can only be explained as the rudiment of Bidder's canal. The
arrangement shown in this reconstruction is found at the kidney
end of every vas efferens which crosses laterally from the testis
to the kidney. At the extreme anterior end of the testis, however,
an altogether different arrangement prevails.
Pig. 29 (PI. 23) is taken from the same series and is cut just
anterior to the testis through about the middle of the fatbodies
(fb.). A duct (ap.), here just dividing into two, runs
alongside and partially through the fat-bodies. Posteriorly to
this level (fig. 28, PI. 23) the two ducts enter the extreme
anterior tip of the testis (£.), into which they pass, branching
out (fig. 27, PI. 23) as the internal sperm-collecting system of
the testis. In this figure the darkly stained mass labelled ap. is
unquestionably the true sexual unita of the frog's kidney. Each straight
tubule ends in such a unit. I am not prepared to say how much of the
straight tubule is homologous with the more posterior collecting-trunks
and how much belongs to the functional tubule of this abortive sexual unit.