HEMICHORDATA CHAP. 
24 
supposed. There is evidence derived from the results of the 
“Siboga” expedition that abyssal animals may migrate into 
comparatively shallow water in the Malay Archipelago. 
Cephalodiscus and Rhabdopleura are remarkable for their 
power of producing buds. In the former these arise from the 
apex of a stalk which 
is given off on the 
ent 
ventral side of the 
body, and they break 
off when they reach 
a certain age; in the 
latter they do not be- 
come free, and a colony 
results, which consists 
of a creeping “ stolon ” 
from which vertical 
branches are given off 
at intervals, each end- 
ing in an individual 
of the colony. Cepha- 
lodiscus forms a gela- 
tinous “house” (Fig. 
9, A), in the passages 
of which are found 
large numbers of the 
ov 
bc3 
Fic. 10.—Longitudinal median section of Cephalodiscus free individuals,  to- 
dodecalophus. a, Anus ; b.c}, b.c®, b.c %, first, second, aie +] Fer 
and third body-cavities ; int, intestine ; m, mouth; Seber With ell 
nch, notochord ; 7.s, central nervous system ; ves, evos and embryos. 
oesophagus ; op, operculum, the ventro-lateral part 7 re Winer e 
of the collar ; ov, ovary ; ovd, pigmented oviduct ; Rhabdopleura (Fig. 
ph, pharynx ; p.p, proboscis-pore ; ps, proboscis ; st, | 2) is protected by 
stomach ; stk, stalk. 
cylindrical tubes, one 
of which corresponds with each individual. 
Cephalodiscus, though no more than two or three millimetres 
in length, is provided with practically all the important organs 
possessed by Balanoglossus. Its proboscis or “buccal shield” 
(Fig. 10, ps) is a large flattened structure, which overhangs and 
entirely conceals the mouth. The anterior body-cavity opens to 
the exterior by two symmetrically placed proboscis-pores (p.p), 
just in front of the tip of the notochord (neh). The collar, 
which has paired body-cavities, is produced dorsally into 4-6 
