REPORT ON CEPHALODISCUS DODECALOPHUS. 



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being perfectly free, and at liberty to wander anywhere along the chambers or externally 

 through the apertures. In some cases they are packed closely together in the cavity, 

 probably from external causes acting after immersion in spirit ; for thin partitions, bridles, 

 and pillars of the semitransparent coenoecium often separate the individuals. The 

 cavities are generally clean, though occasionally a little mud containing sponge and 

 other spicules, including peculiar reticulated fragments apparently of Radiolarians, occurs. 

 This would seem to show that currents of sea- water sweep through these chambers very 

 freely, probably assisted by the active movements of the cilia covering the tentacular 

 plumes. Moreover, in dissecting out the latter, an operation performed with ease, owino- 

 to the friability of the ccenoecium, at first sight it may almost be supposed than an 

 ovigerous envelope containing embryos is before us, so remarkable is the profusion of eggs 

 and animals, and apparently so active is the 

 reproductive function. The aspect of the 

 adults and their terminal buds, the proportion- 

 ally large size of the ova, and other features, 

 however, negative such a supposition. 



Each adult polypide (and they are some- 

 what uniform in size) measures, from the extre- 

 mity of the cephalic plumes to the tip of the 

 pedicle, about two millimetres (woodcut, fig. 2); 

 and of this length the body -proper — that is from 

 the buccal disk to the posterior bulbous region 

 above the pedicle, — is rather more than one 

 millimetre. The body in most is bean- or 

 kidney-shaped (PI. II. fig. 1), generally more 

 rounded and bulbous posteriorly, since there 

 is a tendency to a forward curve behind the 

 pedicle. The dorsal surface is smooth and 

 convex, a distinct constriction, however, being 

 usually evident just behind the anterior region 



bearing the brownish-red pigment-spots. The latter region is generally bulbous and 

 prominent, and in many a slightly elevated median ridge leading to the arms is present. 

 So far as the spirit preparations go, therefore, the external difTorcntiation of the anterior 

 region, called "thoracic" by Lankcster in Rhahdopleura, is indistinct in Cephalvdu^cus, 

 but internally the collar body-cavities are diagnostic. As the pedicle is often curved 

 forward or projected outward at a small angle to the body, the ventral surface is 

 thus rendered comparatively short (PI. III. fig. 2); indeed, in tlioise which arc much 

 bent, the base of the pedicle touches the buccal disk. This contour of the body is 

 interesting in relation to the oblique direction of the cup-like body of Liu-osnma. Wlicn 



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Flo. 2. — Ventral view of Ccpluilodiseus dodtcalophvt, 

 M'Intosb. 



