Volume 1

Text-book of embryology / edited by Walter Heape.

Date:
1914-
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Text-book of embryology / edited by Walter Heape. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

    110/732 (page 74)
    CHAP, relatively small. This Fig. 53.—AstrobilizedScyphis- toma of Aurelia aurita. (After Claus.) /, forkRil lappet of edge of disc of Ephyra; ten, tentacles of Hydra- tuba degeuerating; ieul, rudi- mentary .sense-tentacles of Ephyra. again is a I'eature which we find in many larvae which are adapted for continuous free-swimming lile. The larva never fixes itself, aud eventually tiie lobes of the Ephyra grow out in a circle round the moutli. The whole development is therefore modified along quite similar lines to those exhibited by the Geryonidae, the hydra-tul)a being modified into a floating larva, just as is the hydroid stage of the Geryonidae. When we review what we have learned of the development of Scyphozoa, we are struck at first by the great differences between their life-histories and those of the Hydrozoa. A deeper and closer analysis tends, however, to diminish the supposed differences very much. It has been shown that many Hydroid colonies periodically lose and regenerate the polyps (Allman, 1871-2), {i.e. the swollen distal ends or heads of the hydroids which carry the tentacles and genital organs), that during the winter the polyps are often absent, and that these are regenerated from the basal stumps in Fiu. 54.—All Ephyra larva of Aurelia aurita jjmt after liberation from the strobilized scyphistoiiia. (After Frieileiiiann.) ad, adradial lobe of ring-gut; g.f, gastral filament; int, inter-radial lobo of ring-sinus; I, forked lappet of edge of di.sc ; o.c, oral cone ; jjcr, per-radial lobi) nf ring-sinus ; r, ring-sinus ; sg, sub-genital pit; iejil, sen.se-tentacles.