26 HEMICHORDATA CHAP. 
system and the anus. Each oviduct (ovd) contains dark pigment, 
which is seen through the dorsal skin on removing the tentacular 
Fic. 12.—Small portion of colony of 
Rhabdopleura normani, Allman, 
Lofoten Islands, x 16. a, Anus; 
Pp, proboscis (=buceal disc) ; 7, rod- 
like axis of the adherent part of the 
colony, prolonged into s, the stalks 
of the individuals; sf, stomach; 4, 
the two tentacular arms of the collar. 
(After Sars.) 
arms. Eggs, each enclosed in a 
stalked membrane, occur in num- 
bers in the cavities of the gelatin- 
ous house. The early stages of the 
development are passed through 
inside the tubes; but there is at 
present little other information 
with regard to the embryonic de- 
velopment of the Pterobranchia. 
The specimen obtained by the 
“Siboga ” from Celebes is a male 
colony with dimorphic individuals, 
the reproductive organs being con- 
fined to two-armed zooids with 
vestigial alimentary canal. 
Rhabdopleura differs from 
Cephalodiscus in its much smaller 
size, and it is perhaps due to 
its minuteness that it does not 
possess certain organs found in 
the latter. The stalk is repre- 
sented by a long muscular cord, 
which is merely a narrow part 
of the body. SBasally the stalk 
of each individual passes into a 
common axis, which is for the 
most part attached to the sub- 
stance on which the colony ts 
growing, and is to some extent 
branched. The muscular stalk 
can be contracted into a spiral, 
thereby retracting the animal 
into its tube. The stalks and 
the younger parts of the axis 
which connects them are soft, but 
the older parts secrete a dark brown cuticle, forming a narrow 
1 The diameter of a single individual removed from its tube is given by Fowler 
as ‘123 mm. 
