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

194 EDWIN S. GOODRICH.
although sometimes the epithelium seems to stretch over the
base of the solenocyte tubes for a considerable way. The
coelomic epithelium is not continuous with the wall of the
canal at the tip of the diverticula, but often can be seen in
sections to end with a free and jagged edge. Over the region
where the solenocytes occur there is a gap in the coelomic
epithelium, so that coelomic fluid freely bathes the solenocyte
tubes (figs. 2, 3). That the space in which lie these tubes,
and even the deep pockets described above (p. 193), communicate
with the coalom is evident in specimens injected with
Indian ink.
Since no epithelium covers the solenocytes their true relation
to the coalom cannot be made out for certain in •the
adult. Without going into the question of their development
in this paper, I may say that a careful examination of
M. Legros's excellent preparations has convinced me that in
the very earliest stages of its development the whole rudiment
of the nephridium and solenocytes lies enclosed between
the coelomic epithelium and the atrial wall. There is nothing
unusual in the solenocytes coming into secondary contact
with the coelomic fluid. We know that in the Actinotrocha
larva the nephridium pierces the wall of the preseptal
htomocoel, and the solenocytes project freely in the blood
(8). In many Polychsetes also the nephridium passes through
the coelomic epithelium and the solenocytes lie naked in the
coelomic fluid (6).
To sum up the chieE points in this contribution :—The
careful examination of the nephridia in sections and in the
living state shows that they have no internal opening. The
tubes of the solenocytes pierce the wall of the nephridial
canal, and open into its lumen. The flagellum passes down
the tube into the lumen. The solenocytes are attached to
the wall of the bloodvessels, which expand in this region, and
may surround the canal. Both the bloodvessels and the
nephridial canal are covered by the coelomic epithelium,
being situated between it and the atrial wall. Over that
region which is occupied by the solenocytes there is a gap in