Ambulacra sentence example
- Spencer to have had in its ambulacra an inner as well as an outer series of plates.
- If this be correct, the only change from Edrioaster, as regards the ambulacra, was that in Palaeodiscus the covering-plates could no longer open, but closed permanently over the whole groove, while the podia issued through slits between them.
- The thecal plates, however irregular in some species, always show defined basals and a distinct plate ("radial") at the end of each ambulacrum; they are in all cases so far affected by pentamerous symmetry that their sutures never cross the ambulacra.
- The stereom of the radials and deltoids on each side of the ambulacra is thrown into folds, running across the radio-deltoid FIG.
- The position of the pores near the centre of the ambulacrals in Bothriocidaris need not be regarded as primitive, since other early Palaeozoic genera, not to mention the young of living forms, show that the podia originally passed out between the plates, and were only gradually surrounded by their substance; thus the original structure of the echinoid ambulacra differed from that of the early asteroid in the position of the radial vessels and nerves, which here lie beneath the plates instead of outside them.Advertisement