28 HEMICHORDATA CHAP. 
would indicate a near relationship between Cephalodiscus and 
Phoronis. 
Phoronis is a small tubicolous animal, of gregarious habits, 
which has usually been regarded as related to the Gephyrea. Its 
body ends in a plume of cilated tentacles, which can be pro- 
truded from its tube, and the anus is on the dorsal side, not 
far from the mouth. In both these respects it agrees with 
Cephalodiscus, but a more striking simi- 
larity is asserted by Masterman to exist 
between the latter and Actinotrocha, the 
larval stage of Phoronis. The prae-oral 
ciliated hood (Fig. 14) of Actinotrocha is 
regarded as the proboscis, and it contains’ 
a median cavity, traversed, like that of 
Balanoglossus, by muscular fibres. The 
collar is the region between the con- 
stricted neck and an oblique lne, parallel 
to and immediately behind the series of 
tentacles, which thus belong to the collar. 
This division has a collar-cavity which is 
said to be distinct from the prae-oral 
cavity, and is separated by a septum from 
the posterior body -cavity. Its dorsal 
epidermis contains the central nervous 
system (7.8), which is connected with 
a system of nerves resembling those 
of Balanoglossus. A median  diverti- 
culum of the alimentary canal of this 
part may be compared with the noto- 
‘ f chord of that animal, but there are no 
es cintosh, "Phitipping Sill-slits, 
Islands, x about 2. The remainder of the body of Actino- 
site oP om trocha corresponds with the trunk of 
Balanoglossus. Its body-cavity is distinct 
from that of the collar, and is divided by a ventral mesentery, 
though not by a dorsal mesentery. A noteworthy fact is that 
both Actinotrocha and Tornaria swim by means of a ring of 
strong cilia or membranellae* which surrounds the anus. 
Important memoirs on the structure of Actinotrocha have 
1 Giep.s12: 
