THE ANATOMY OF PHORONIS AUSTRALIS. 129 
each end is more or less spirally wound round a slight cone. 
The tentacles vary in length, those of the inner coils being 
successively shorter than those of the outer, visible rows. In 
this species there are three coils on each side. 
Whereas the outer series of tentacles is perfectly con- 
tinuous on the oral side, the corresponding inner series, that 
between mouth and anus, is incomplete, there being a gap at 
the dorsal mid-line, as shown ‘in figs. 12, 7. The tentacles to 
the right and left of the gap are the youngest of the whole 
series ; and it appears that the whole number of tentacles in- 
creases with the age of the animal. They are exceedingly 
numerous in Ph. australis and Buskii, whilst in Ph. 
Kowalevskyi (Caldwell) they are, in my specimens, about 
one hundred in number. 
The bases of the tentacles are connected together for about one 
quarter or about one third of their whole length, thus forming 
the so-called “ tentacular-membrane”’ (figs. 5, 6, 4.), as is the 
case with some Polyzoa: but, as will be seen, there is in 
Phoronis no true “membrane.” The ends of the tentacles are 
free, and can be in life, doubtless, moved about to some extent. 
In Ph. hippocrepia (Strethill Wright), Dyster has figured 
them gracefully curved, the outer series outwards, the inner 
series arching over the dorsal surface. 
Each tentacle has the following structure, as seen in transverse 
section, fig. 13. The epidermis consists of a single row of cells 
over the greater part of the surface, but on the inner surface 
is two or three cells deep, and those of the outer layer 
here carry long cilia ; within the epidermis is a ring of tissue, 
which forms the skeleton, and which Caldwell has shown to be 
mesoblastic in origin. This encloses a spacious cavity, con- 
tinuous below with the coelom; and in it lies, on the inner 
side, a blood-vessel. This vessel passes to the extremity of the 
tentacle, and is single throughout its extent, ending blindly at 
the tip, but dividing into two exceedingly short branches in 
the lophophore, as will be described below. 
A nerve passes up each tentacle on its inner side. At the 
base of the tentacular crown, in the region of the “tentacular 
