A treatise on zoology . as. By the removal of some of thepodia, the ambulacral grooves may be seen to lie outside a seriesof pairs of narrow j^lates—the ambulacral ossicles (Fig. III.). The two series of ossicles meetin the middle line ; laterallythey abut against a rowof adambulacral ossicles, be-yond which are further rowsof interambulacral and mar-ginal ossicles, all of whichare comparatively small. Theossicles are protected by spines and pedicellariae similar to, butsimpler than, those of Echinoidea. The Oral Skeleton (or actinostomial ring) consists of a solidcalcareous ring around the mo
A treatise on zoology . as. By the removal of some of thepodia, the ambulacral grooves may be seen to lie outside a seriesof pairs of narrow j^lates—the ambulacral ossicles (Fig. III.). The two series of ossicles meetin the middle line ; laterallythey abut against a rowof adambulacral ossicles, be-yond which are further rowsof interambulacral and mar-ginal ossicles, all of whichare comparatively small. Theossicles are protected by spines and pedicellariae similar to, butsimpler than, those of Echinoidea. The Oral Skeleton (or actinostomial ring) consists of a solidcalcareous ring around the mouth. It is composed of thirty platesin a quinqueradiate starfish, there being always six times as manyplates as there are rays. Each segment of the oral skeleton con-sists of two pairs of ambulacral, and of one pair of adambulacralossicles. In Asterias the ambulacral plates are more prominentthan the adambulacrals, and project into the oral cavity. Themouth armature is therefore on the ambulacral type (Viguier,52). 16. Fig. III. Asterias ruhens, ambulacral and adambulacral , apertures for podia. 242 THE STELLEROWEA The Alimentary System consists of a mouth at the centre ofthe actinal surface of the starfish. The oesophagus is very short
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
