36 MR. W. K. HUTTON ON THE § ~ [ Jan. 20, 
Although nowadays, in virtue of our knowledge of the totally 
distinct modes of development of the tentacles in Phoronis and 
the Sipunculids, it does not seem possible to institute any 
homology between the lophophoral crowns of Phoronis and 
Phymosoma, yet it may be of interest to note that in the species 
of Sipunculid under consideration the homologue of the pigmented 
epithelium, which in Phymosoma covers Shipley’s ‘ preeoral lobe,” 
is to be found in that layer of pigmented cells (Plate VIII. 
fig. 12, S.E.) which forms the dorsal wall of the epineural canal 
as well as in that layer continuous with it, bounding the anterior 
surface of the brain (fig. 13, E.). 
Nephridia. 
These are small (Plate VI. fig. 2, B.T.), measuring less than the 
twentieth part of the length of the worm; the right nephridium 
is the longer and more convoluted of the two. Hach organ 1s 
retort-shaped (Plate VIII. fig. 17), having a bulbous portion (C) 
attached to the body-wall, and a tubular part (D) which, arising 
from the posterior part of the bulb, bends round it mesially and 
projects freely forwards into the ccelom. The wall of the bulb is 
thin, covered externally by the cells of the peritoneum (A, fig. 18), 
and internally by a single layer of granular-looking columnar 
epithelium (C, fig. 18); it is composed of slender intercrossing 
muscular bands. The cavity of the bulb is packed with fine 
vesicles (H, fig. 18), which, it will be seen, are derived from the 
secreting epithelium of the tubular portion of the nephridium. 
The bulb communicates with the exterior by a fine canal (A, fig. 17), 
lined with a small-celled epithelium, which pierces the body-wall 
immediately in front of the anus, and its cavity is, further, 
placed in connection with the ceelomic space through a slit-like 
opening (B, fig. 17) in front of the excretory canal. The lips of 
this opening, lined with ciliated epithelium, le between the body- 
wall and the bulbous part of the nephridium, and are concealed 
by its overhanging anterior extremity. The tubular portion of 
the organ has a wall which is formed by a peritoneal lameiia, 
heneath which is a layer of muscles (B, fig. 18). This muscular 
layer consists of a meshwork of strands, between interstices of which 
the lining-epithelium bulges outwards, forming little crypts lned 
with a single layer of secretory cells (C). In cross section there 
are seen projecting into the lumen of the tube feathery columns 
of cells (D, fig. 18), which have an appearance comparable to that 
of goblet-cells. The nucleus is small and irregular in shape, 
placed basally; while the cell-contents may be seen to become 
clearer near the free margin, and are evidently extruded ultimately 
as the thin-walled vesicles which are found filling the lumen of 
the organ. 
Shipley aptly compares the process, which takes place also,in 
Phymosoma, to the formation of the granules excreted by the 
cells of the mammary gland. 
