A treatise on zoology . ween these two circlets ap|)earthe radials, u|)()ri tlu^ shouhhus of whicli the five adoral interradialsthen rest (Fig. XXXIII. 2), forming a ])yraniid closed over tliooral centre, but soon opening at the apex to expose the entninceto the mouth (terita(Miiar vestibuU;)- l* posterior of th(»s(^ platessurrounds the hy(lroj)ore. At a nioi(^ advanced stage tliev becomeseparated from the radials by aml)uhicrals and interaml)ulacrals Fi<;. XXXII. TfKiiili f Mdrslpocriiiiis rinllntns, sliow-iiiH iiicijrponitidii of Avih, umlnilucnils, withlAiiih, , li»
A treatise on zoology . ween these two circlets ap|)earthe radials, u|)()ri tlu^ shouhhus of whicli the five adoral interradialsthen rest (Fig. XXXIII. 2), forming a ])yraniid closed over tliooral centre, but soon opening at the apex to expose the entninceto the mouth (terita(Miiar vestibuU;)- l* posterior of th(»s(^ platessurrounds the hy(lroj)ore. At a nioi(^ advanced stage tliev becomeseparated from the radials by aml)uhicrals and interaml)ulacrals Fi<;. XXXII. TfKiiili f Mdrslpocriiiiis rinllntns, sliow-iiiH iiicijrponitidii of Avih, umlnilucnils, withlAiiih, , li»t\vtfii tlitMii ;iiii. murks anal intmnnliiis, with its lur^;trinttimiiiliiiliicriih. (AttiT inWachsiiiulli Hi .Sprinxt^r, IfiJl.) X jl. THE CRINOIDEA 125 (Fi<;. XXXllI. ;?)), and finally, in most species of yintedon, arercsorbed (cf. Fig. XXX. 4). These plates are called oralia (0).Their prominence in eai-ly sla^^cs shows them to be primaryelements of the theca, probably well developed in the adult of. Fig. XXXlir. Doveloi)iiieiit of orals in Autedou. 1 (alter Bury), IJi still visible, no IIR yet formed. 2(after Allinan), 0 closed ; between them and y^yiarethe devel()j)inj^ yiyi. 3 (after Allinan), >oj)en,exi)osinu: oral tentacles; no arms yet exist. 4 (after W. B. Carpenter), O now sej)arated fiomlUi by nil, which su])i)ort arms, f) (after W. B. Carpenter), arms cut off above lirst brachial soas to show O, which now surround the mouth ; tli(! shaded portion represents integument, inwhich ambulacrals and interambulacrals are develoi)ed. Note also <rradiuil decreasH in size of yjy;. A further stage in oral liistoiy is seen in 4, which is from another species. primitive forms. Five triangular plates that cover the mouth inthe recent IIolopus, Hyocrinus, lihizocrinns, and Thaumafocrinus,are by all writers homologised with orals (Fig. XXXIV.). Inall Antedonidae, Bathycrinus, and Calamociinus, they are almost Amb
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
