For Belgium the Faune belge of Baron De Selys-Longchamps (8vo, 1842), old as it is, remains the classical work, though the Planches colorises des oiseaux de la Belgique of M.
29) under the names of Mergus anatarius, Clangula angustirostris, and Anas (Clangula) mergoides, as though they were a distinct species; but the remarks of De Selys-Longchamps (Bull.
These associations of individuals can hardly be the result of the metamorphosis of a corresponding number of larvae, but are probably due to a spontaneous fragmentation of the adult animals, each such fragment developing into a complete Phoronis (De Selys-Longchamps).
2) shows: the mouth (m), continuous on either side with the groove between the two series of tentacles; the anus (a), in the middle line, at no great distance from the mouth; a transversely elongated epistome (ep), between the mouth and the anus; and, in the concavity of the lophophore, the apertures of the nephridia (n.o.) which, according to De Selys-Longchamps, open into the two large sensory or glandular "lophophoral organs " the orifices of which are seen at gl.
According to researches in 1907 by De Selys-Longchamps, the blood is driven by the afferent vessel (af) to a crescentic lophophoral vessel (d.v.) which supplies the tentacles.
This view of the surfaces is, however, disputed by De Selys-Longchamps, who regards the aboral extremity of the adult as the posterior end.