A treatise on zoology . f the ambulacra, even in their least specialised form, atonce remove the type from primitive simplicity, and place it on aroad different from that traversed by other Pelmatozoa. The evi-dence suggests the existence of a circumoesophageal water-ring, withfive perradial canals, and their associated nerves and blood-vessels,passing between or below the thecal plates, and underlying aciliated food-groove, which was covered by an alternating seriesof movable plates (covering-plates = ambulacrals of Crinoidea, butprobably not those of Echinoidea and Asteroidea). Pores between
A treatise on zoology . f the ambulacra, even in their least specialised form, atonce remove the type from primitive simplicity, and place it on aroad different from that traversed by other Pelmatozoa. The evi-dence suggests the existence of a circumoesophageal water-ring, withfive perradial canals, and their associated nerves and blood-vessels,passing between or below the thecal plates, and underlying aciliated food-groove, which was covered by an alternating seriesof movable plates (covering-plates = ambulacrals of Crinoidea, butprobably not those of Echinoidea and Asteroidea). Pores betweenthe plates lining or flooring the groove (adambulacrals of Pelma-tozoa, but perhaps = superambulacrals of Asteroidea) permittedthe passage either of podia or ampullae. In Cystidea, Blastoidea,and primitive Crinoidea, on the other hand, there was a free exitfor the ambulacral organs only through the peristome; in fact,Blastoidea and Cystidea present no evidence that they possessedperradial water-vessels and podia at
Size: 1653px × 1512px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
