432 ZOOLOGY 
division of its body into three regions,—the proboscis, collar, 
and trunk,—and in the arrangement of its coelomic cavities and 
the possession of proboscis- and collar-pores. Moreover, it is 
provided with gill-slits, with a diverticulum of the alimentary 
Fie, 249.—Longitudinal section of an 
adult Cephalodiscus, supposed to 
be taken sufficiently on one side 
of the middle line to allow of the 
representation of one of the ovaries, 
and of one of the proboscis pores. 
After Harmer. 
. Proboscis. 
i 7. Ovary. 
21, Body-cavity of proboscis. 8. Anus. 
2°. Body-cavity of collar. 9. Pigmented oviduct. 
28, Body-cavity of trunk. 10. Central nervous system. 
3. Notochord (really visible only ina 11. One of the proboscis pores. 
median section). 12. Mouth. 
4. Operculum. 13. Pharynx or branchial region of gut. 
5. Pedicle or stalk cut through. 14. Oesophagus. 
6. Intestine. 15. Stomach. 
canal (notochord) growing into the proboscis stalk, and with 
a nervous system which closely resembles that of Balanoglossus. 
Cephalodiscus has only been found once. It was dredged 
in the Straits of Magellan by the “Challenger” from a depth 
of 245 fathoms. The various “ polypides,” with their budding 
pedicles, live inside a coenoecium or tubular case secreted around 
them, in much the same way as Appendicularia secretes its 
“house.” 
Sub-class III. RHABDOPLEURIDA. 
CHARACTERISTICS.—Gill-slits and proboscis pore absent. The 
intestine has a neural flexure. There are two tentacular 
plumes having the same relation as in the Cephalodiscida. 
