164 THE VOYAGE OF H.M.S. CHALLENGER, 
are smaller, and have no directly depending ridges and filaments, but which, diverging a 
little, course outwards, with slight contortion of their borders, to form, after a short 
distance, dense masses of coils on the faces of the mesenteries. The borders of the quater- 
nary mesenteries and filaments arise from the under surface of the disc membrane still 
further out, and hence their filament tissue does not touch that of the stomach anywhere ; 
they pass out, as do the foregoing, and are similarly distributed. Processes of the 
muscles of the septa are prolonged into the tentacles, and near the borders of the 
mesenteries, where the tentacles arise, strong transverse fibres are developed in the 
mesenteries, which, when traced upwards, are seen to belong to the same system as the 
circular muscles of the tentacles. The tentacles, when cut across in decalcified sections, 
show the two laminze which invested on either side the septa over which they are placed, 
crossing their bases. The tertiary mesenteries sometimes in Mlabellum alabastrum bear 
a few ova, sometimes not. The ova developed on primary and secondary mesenteries are 
abundant in the deep chambers in the apex of the corallum, and also those of the 
tertiary, which also pass far down. The sexes are distinct in all the specimens of Flabel- 
lum which I have dissected. The male elements are enclosed in the mesenterial masses, 
just like the ova, and apparently fill up all the lower chambers of the corallum solidly. 
In Flabellum japonicum there are dark pigmented glands in the ectoderm, as in 
Sagartia. The ova commence just below the muscular arch of the mesentery, and 
behind the dependent spiral coil of mesenterial filament. The coverings of soft tissue on 
the faces of the septa are excessively thin, and consist of simple endoderm and mesoderm, 
never having muscles in their substance or anything like mesenterial filaments attached 
to them. They are evidently foldings up of the lming membranes of the interseptal 
chambers raised up from the wall. In each fold is developed a septum. In the corallum 
the septa themselves are seen in the lower part to look like folds. 
A diagrammatic representation of the arrangement of the mesenteries and septa, and 
of the disposition of the layers of tissue composing them is given on Plate XVI. fig. 10. 
The ideal transverse section which it represents is supposed to be taken at the level of 
the margin of the corallum so as to pass just below the soft tissue membrane composing 
the disc. Hence soft tissues are represented as occurring on the outside of the corallum. 
The section, further, is taken above the level at which the chambers between the 
mesenteries open mto the stomach. The mesenterial muscles are placed on the sides of 
the mesodermal plates of the mesenteries which lie next the septa, whilst the mesenterial 
filaments lie on the opposite sides of these. 
One tentacle in section is introduced into the diagram in order to show the relation 
of the tentacle to the septum lying beneath it and to its investing layers. 
Flabellum angulare, Moseley (Proc. Roy. Soc., 1876, p. 556). (PI. VI. figs. 2, 2a, 20.) 
The corallum is thin and fragile, and of a pearly white, covered externally with a 
