. The Cambridge natural history. Zoology. 48o ECHINODERMATA OPHIUROIDEA ventral and lateral plates, guarded each by a valve-like plate called the "; In Ophiothrix they are covered with sense-organs, each consisting of a hillock-like elevation of the ectoderm, in which are cells carrying long stiff sense-hairs. In most Ophiuroids such organs are not present, though abundant scattered sense-cells occur, and the outer surface of the tube-feet and the lining of certain pockets called " genital bursae" (Fig. 208, c/.b) are the only portions of the surface where th
. The Cambridge natural history. Zoology. 48o ECHINODERMATA OPHIUROIDEA ventral and lateral plates, guarded each by a valve-like plate called the "; In Ophiothrix they are covered with sense-organs, each consisting of a hillock-like elevation of the ectoderm, in which are cells carrying long stiff sense-hairs. In most Ophiuroids such organs are not present, though abundant scattered sense-cells occur, and the outer surface of the tube-feet and the lining of certain pockets called " genital bursae" (Fig. 208, c/.b) are the only portions of the surface where the ectoderm persists. Everywhere else, although present lateral arm upper arm plate. ect. â ⢠⢠tentacle ,^ scales. Ij ; underarm '. .. plate. perih. Fig, 209.âDiagrammatic transverse section of the arm of an Ophiuroid. coe, Dorsal coeloniic canal; ect, ectoderm covering the tube-foot; ep, epineural canal; , pedal ganglion ; L, nerve-cord ; muse, longitudinal muscles attaching one vertebra to the next; , radial nerve-oord_; perih, radial perihaemal canal; pod, podium (tube-foot); sp, lateral spines ; , radial water-vascular canal. in the young, it disappears, leaving as remnants a few nuclei here and there attached to the under side of the cuticle.^ The greater part of the section of the arm is occupied by a disc-like ossicle called the "; Each vertebra articulates with its predecessor and successor by cup-and-ball joints, and it is connected to each of them by four powerful longitudinal muscles. Above, its outline is notched by a groove, in which lies an extension of the coelom of the disc (Fig. 209, coe), but contains no outgrowth of the alimentary canal, as is the case in Asteroidea. The vertebra is also grooved below, and in this lower groove are contained the radial water - vascular canal ^ In the more primitive Opliiuroidea (Streptophiurae) it persists all over the body ; in Cladophiurae it is foun
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
