2), which is attached to the wall of the space, or rhynchocoel, in which the proboscis moves about.
The rhynchocoel is formed by a split which appears in the mesoblast surrounding the epiblastic pit which is the forerunner of the proboscis.
The muscular walls of the rhynchocoel, which by their transverse contractions serve to bring about eversion of the proboscis in the way above traced, are attached to the musculature of the head just in front of the ganglionic commissures (fig.
In nearly all Nemertines the rhynchocoel extends backwards as far as the posterior extremity, just above the anus; in Cannella it is limited to the anterior bodyregion.
(From Burger.) i, Opening of proboscis; 2, cephalic glands running to frontal organ; 3, dorsal commissure of brain; 4, cerebral organ; 5, upper dorsal nerve; 6, under dorsal nerve; 7, rhynchocoelic blood-vessel; 8, fore-gut; 9, rhynchocoel; to, nerve to proboscis; 11, proboscis; 12, genital sac; 13, genital pore; 14, mid-gut; 15, circular nerves; 16, pore of excretory system; 17, lateral organ; 18, excretory canal; 19, lateral vessel; 20,.