The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . t—which is used up later on in the development. Many sugges-tions have been made as to the homology of the elaeoblast. Themost probable is that it is the disappearing rudiment of the tailfound in the larval condition of most ,The family Octacnemidae includes the single remarkable genusOctacnemus, found during the Challenger expedition, and first„ _ described by Moseley (29). It is now known in both a id*^^ solitary and an aggregated form, and was regarded by™ ^^* Herdman as a dee
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . t—which is used up later on in the development. Many sugges-tions have been made as to the homology of the elaeoblast. Themost probable is that it is the disappearing rudiment of the tailfound in the larval condition of most ,The family Octacnemidae includes the single remarkable genusOctacnemus, found during the Challenger expedition, and first„ _ described by Moseley (29). It is now known in both a id*^^ solitary and an aggregated form, and was regarded by™ ^^* Herdman as a deep-sea representative of the pelagicSalpidae, possibly fixed; or, better, as related to the primitive fixedforms from which Salpidae have been derived. Metcalf. however,has shown that the aggregated form of 0. palagoniensis. which he hasdescribed, is more nearly related to the Clavelinidae amongstAscidiacea. The body is somewhat discoid, with its margin pro-longed to form eight tapering processes (fig. 24), on to which themuscle bands of the mantle are continued. Tfie alimentary canal At. At,, Fig. 24.—, Solitary form (after Herdman). B, Aggregated form (afterMetcalf).(1. Anus. m, Mouth. Atrial aperture. as. Oesophagus. - Branchial sac. , Peribranchial cavity, , Gill slit. St, Stolon. forms a compact nucleus (fig. 24, A); the endostyle is very short;and the dorsal lamina is also reduced. The reproduction and life-history are entirely unknown. Octacnemus bylhius was lound by the Challenger expedition in the South Pacific at depths of 1070 and2160 fathoms, and Metcalf has since described a new species. Opatagoniensis from 1050 fathoms off the Patagonian coast, in which there is an aggregated form (fig. 24, B) consisting ol indiWduals unitedby a stolon composed of test and III.—Ascidiacea Fixed or free-swimming simple or compound Ascidians which inthe adult are never provided with a tail and have no trace of anotochord. The free-sw
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectencyclo, bookyear1910
