. Fig. 3. Willia mutabilis. The radial canal system of an early stage, showing commence- ment of torsion of the umbrella; also a single branch to each of the eight radial canals. primary radial canals, whereas the four others are lateral branches of the former. Presumably therefore a still younger stage exists, with only four radial canals, as in young specimens of Proboscidactyla. In the third specimen of this sample a torsion of the umbrella has just commenced (Fig. 3); the course of the four primary canals is not exactly perradial in relation to the stomach, and the corresponding tentacles
. Fig. 3. Willia mutabilis. The radial canal system of an early stage, showing commence- ment of torsion of the umbrella; also a single branch to each of the eight radial canals. primary radial canals, whereas the four others are lateral branches of the former. Presumably therefore a still younger stage exists, with only four radial canals, as in young specimens of Proboscidactyla. In the third specimen of this sample a torsion of the umbrella has just commenced (Fig. 3); the course of the four primary canals is not exactly perradial in relation to the stomach, and the corresponding tentacles are a little displaced, in a clockwise direction when the medusa is seen from above. The four interradial basal bulbs have developed into tentacles which, however, are distinctly smaller than the four perradial ones; moreover, there is a lateral branch to each of the eight radial canals, issuing somewhat nearer to the umbrella-margin than to the stomach, all to the same side; at the termina- tion of each of these lateral branches is a very small basal bulb, and above each of these a cluster of nematocysts. There are several slightly older specimens in which the two radial canals issuing
Size: 2245px × 2227px
Photo credit: © The Bookworm Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, booksubjectocean, booksubjectscientificexpediti
