The porifera and coelentera . also be present(Podocoryne), or very numeroustentacles arranged in four per-radial groups (Bougainvillea) ;even hiuidreds may be present(Callitiaxa), arranged apparentlywithout reference to specialradii. Tlieir bases are generallysurrounded l)y a thickened bull)of ectoderm, containing sensorycells and numerous sense organs of the Anthomedusae are ocelli. These consisteither of a few pigment cells, hardly grouped into an organ(Euphy!?a), or of pigment cells grouped into a definite retina,which possesses (Lizzia, Fig. 11) or lacks (Sarsia) a lens. Th
The porifera and coelentera . also be present(Podocoryne), or very numeroustentacles arranged in four per-radial groups (Bougainvillea) ;even hiuidreds may be present(Callitiaxa), arranged apparentlywithout reference to specialradii. Tlieir bases are generallysurrounded l)y a thickened bull)of ectoderm, containing sensorycells and numerous sense organs of the Anthomedusae are ocelli. These consisteither of a few pigment cells, hardly grouped into an organ(Euphy!?a), or of pigment cells grouped into a definite retina,which possesses (Lizzia, Fig. 11) or lacks (Sarsia) a lens. They are i)lace(l on the bulb of the tentacle, and are generallyon its exumbral face, but are on the subumbral face in generawhich normally carry their tentacles reflexed (Lizzia). The (jastric cavitij generally lies in the bell, but may at the root of the manubrium (Lar). It often exhibitsa prolongation upwards into the substance of the mesogloea of theexumbrella, a relic of the endoderm of the coenosarcal tube by. Fio. 24. —Diajiraiii of 7i(/»»/iiniiitHlusoiils biiilded from a blastostjieAUiimii.) THE HYDROMEDUSAE 17 which its coeleiiteron originally communicated with that of thecolony from which it was budded. The radial canals are generally four in number, and are thenperradial ; but four interradial canals are also developed in somecases (Cladonema). Six are normally presented by Clavatella( = Eleutheria). In Lar ( = Willsia) six are also present, whichbifurcate twice; theie are thus twenty-four openings into thecircular canal. The generative cells (gonads) lie in the wall of the manubrium,between the ectoderm and the mesogloea, or in the ectoderm itself ;they rarely reach on to the subumbrella (Nemopsis). They are
Size: 1504px × 1662px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
