The trunk contains paired third body-cavities (_b.c^3_), the septum between which and the collar-cavities is slightly behind the line of origin of the operculum. Two ovaries (_ov_) are situated between the pharynx and the last part of the intestine, each opening to the exterior dorsally between the central nervous {26}system and the anus. Each oviduct (_ovd_) contains dark pigment, which is seen through the dorsal skin on removing the tentacular arms. Eggs, each enclosed in a stalked membrane, occur in numbers in the cavities of the gelatinous 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 development of the Pterobranchia. The specimen obtained by the "Siboga" from Celebes is a male colony with dimorphic individuals, the reproductive organs being confined to two-armed zooids with vestigial alimentary canal. [Illustration: FIG. 12.—Small portion of colony of _Rhabdopleura normani_, Allman, Lofoten Islands, × 16. _a_, Anus; _p_, proboscis (= buccal disc); _r_, rod-like axis of the adherent part of the colony, prolonged into _s_, the stalks of the individuals; _st_, stomach; _t_, the two tentacular arms of the collar. (After Sars.)] _Rhabdopleura_ differs from _Cephalodiscus_ in its much smaller size,[48] and it is perhaps due to its minuteness that it does not possess certain organs found in the latter. The stalk is represented by a long muscular cord, which is merely a narrow part of the body. Basally the stalk of each individual passes into a common axis, which is for the most part attached to the substance on which the colony is 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 {27}tube which becomes embedded in the adherent wall of the outer tube. The thin dark axis, to which the name _Rhabdopleura_ refers, is the feature by which the animal can most readily be recognised without magnification. The outer transparent tube is constructed by the proboscis, or buccal shield, the secretion of which appears to be intermittent, so that the tube consists of a series of rings piled on one another. The animal crawls up the inside of its tube by means of its proboscis, while it is retracted by means of the muscles of its stalk.