On the Structure of the Excretory Organs of Amphioxus. Part 2.—The ...

190 EDWIN S. GOODRICH.
focussed to the lower surface; the nuclei of the wall are again
visible. There is no opening.
Innumerable figures could be given of series of sectious all
telling the same story. But the critic will say : if the diverticula
are really closed, sections taken at right angles through
their tip should show the tubes cut across embedded in the
thickness of the wall. Such sections are not difficult to find,
and I figure several on Plates 12 and 13.
Figs. 10 and 12 represent two consecutive sections across
the tip of a branch. In the fh'sb are seen the tubes entering
the wall, while the next (fig. 12) strikes the lumen. A small
part of this figure is shown slightly diagrammatised (fig. 11)
on a larger scale. Again three consecutive sections are
drawn in figs. 15, 16, and 17. Here two sections cut through
the solid wall before the lumen is reached. Lastly, fig. 18
represents a section through two adjacent processes, one of
which has been cut so as to expose the lumen, while the other
shows very clearly the soleuocyte tubes piercing the wall aud
embedded in its cytoplasm.
The evidence of all these sections is quite unequivocal; it
would serve no good purpose to multiply instances; there is
no opening, the wall is continuous, and is traversed by the
tubes of the solenocytes.
But there is other evidence of a different nature leading to
the same conclusion. I have observed in a living nepliridium
the fluid inside the nephridhil canal so compressed, perhaps
by the overlying cover-glass, that it dilated the tip of the
diverticulum so as to give rise to a bulgiug vesicle at its
extremity. Now, such a swelling could obviously not be
formed if the tip were open.
We may now turn to injectious to corroborate our view. I
have receutly injected the dorsal hyperbranchial coslom with
Indian ink. The minute black particles were held in suspension
in sea-water. Such a fluid, if introduced with a
hypodermic syringe, can be made to fill the coslom. It is
clear that if the nephridium communicated with the coslom
the ink would penetrate into the canal; this would happen