THE ANATOMY OF PHORONIS AUSTRALIS. 133 
tinuously, but in groups, giving rise to the appearance of 
striz, in surface view. 
The celomic epithelium consists of pavement-cells, with 
prominent nuclei. 
In the aboral bulbous region of the body, the body 
wall differs somewhat in structure (fig. 10). The epidermal 
cells are considerably larger, and no glandular cells, or very 
few, are present; below the basement tissue comes the 
longitudinal muscular layer ; the circular muscles being here 
within them. McIntosh noted this inversion in his Preliminary 
Note, in 1881 (18). 
The epidermis covering the nerve-band will be described in 
dealing with the nervous system. 
The Nervous System.—As this system lies immediately 
below the epidermis, as Caldwell was the first to observe, it 
will be convenient to describe it at once. 
Passing aborally from the lophophoral ridge, the basement 
tissue is seen, in longitudinal sections, to be separated from 
the epidermis by a narrow layer of granular substance which 
is not stained in borax carmine (fig. 15, N.). Careful observa- 
tion reveals in this granular layer a few rounded nuclei 
belonging to small cells (nerve-cells), and numerous delicate 
fibres crossing the granular substance from the overlying 
epidermal cells. Whether these are nerve-fibres going to the 
epidermal cells, or whether they are exceedingly fine prolonga- 
tions of the bases of the latter I do not know. This is the 
nerve-band which has the following distribution : it follows 
the ridge of the lophophore, passing all round the oral side 
of the animal, and curves round at the side of the nephridial 
ridges, following the spiral course of the lophophore ; it always 
keeps along the outer series of tentacles (whilst the glandular 
ridge lies along the inner series). From this band of nerve- 
tissue a nerve goes to each tentacle, passing along its inner 
surface; a nerve goes to each nephridium; and, as we have 
seen, there isa nervous layer in the epistome, this being the 
only representative of a dorsally placed portion of the nervous 
18 © Proc. Roy. Soc. Edin.,’ 1881. 
