I8r 
mound along the dorsal surface of the body; the anus is a 
large gaping slit at the anterior end of the visceral mass. 
The gill-slit is situated postero-ventrally to the collar canal 
on each side of the body ; it is an oblique slit, sloping antero- 
ventrally as seen from the outside. It is only slightly larger 
than the collar pore, and is set at about the same transverse 
level of the body as the red line of the shield in cases where 
the posterior lobe of the shield is backwardly directed. The 
side of the post-oral lamella flaps over the external openings 
of the coliar canal and gill-slit. | 
The stolon arises, on an average of cases, in the position in 
which it is shown in fig. 4, plate 2, but its point of origin is not 
constant, being sometimes nearer the mouth and sometimes 
nearer the hind end of the visceral mass than is shown in the 
figure. The stolon is longer than the whole body, plumes 
included, and may be as much as twice the length of the body 
if the polypide died with its stolon well extended. In the 
latter case the stolon 1s thin and free from superficial wrinkles. 
The number of buds usually found on the end of the stolon 
varies from two to five. 
The average measurements of the polypides of Cephalo- 
discus gilchristi are as follows :—From end of visceral mass to 
anus, Imm.; from end of visceral mass to front of buccal 
shield, 1°5 mm. ; from end of visceral mass to front of plumes, 
18 mm. 
Parasites.—Occurring very commonly in the stomach of C. . 
gilchristt is a parasitic Copepod which almost fills the cavity 
and leaves very little room for food material. As a rule but 
one Copepod is found in the stomach; in one case two were 
found, but neither of these was fully grown. Sometimes the 
stomach contains an adult female and four free eggs, or a 
female and four embryos, or four embryos of a later stage, 
without the mother. Mature females are common, but no 
adult male has been encountered ; possibly the adult male is 
free-living. 
Dr. W. T. Calman has been good enough to examine this 
parasite for me, and he points our that it comes within the 
family Ascidicolide, Copepods parasitic mainly in the gut of 
Tunicates, and that it is most nearly allied to Enterognathus, 
a parasite described by Giesbrecht from the gut of Comatula. 
The parasite of Cephalodiscus is more degenerate than Entero- 
gnathus. The segmentation of the body is not clearly marked, 
the jaws are much reduced, the thoracic limbs are stout and 
stunted, and there are no projecting egg-sacs. 
Buccal Shield.—The buccal shield of a well-expanded poly- 
pide of C. gelchristz (see text-fig. 1, F) measures about °66 mm. 
