DEVELOPMENTAL ANALYSIS OF SCYPHOMEDUSAE

摘要: Summary The eggs of the scyphomedusae vary in size from 0–03 to 0–3 mm. diameter, a variation thousand-fold volume. Type gastrulation is correlated fairly closely with egg size, smallest gastrulating by unipolar ingression, largest complete or partial invagination, while intermediate gastrulate combined process ingression and invagination. The nature subsequent development equally type gastrulation. become vermiform planula larvae incapable constituting polyp directly, intermediate-sized form planulae which polyps scyphistomae, larger may occasionally actinula so without having had an active existence, develop directly into ephyra-medusa, omitting scyphistoma stage entirely. In case smallest, smaller types, blastula stages have capacity grow as such accompanying progress differentiation. Budding occur even at stage. The develops four, sometimes six, gastric pouches, forms tentacles rim oral disc, usually order 2, 4, 8, 12, 16, further addition fours attain many 32. It consists head stalk, though either part be much longer. Outgrowths body wall near junction stalk pedal stolons for attachment, buds. Buds liberated free-swimming pseudo-planulae, attached parent then liberated, ends long stolons. statoblast function formed successively beneath disc. Tentacles fully grown constrict off, move away pseudo-planulae give rise new polyps. There are regional differences pieces regenerate whole Isolated endoderm has no reconstitute polyp. ectoderm any level can perfect whole. The strobilation depends upon shape column. When shallow long, monodisc, resulting one, two ephyrae. large more less columnar, segmental constrictions appear, typically poly-disc. segments polydisc strobila do not necessarily ephyrae, but themselves scyphistomae reattached typical least, initiation attainment accumulation food reserves, certain critical low temperature. Most ephyrae eight lappets, first ephyra formed, that is, than eight, last numbers. initial number, their corresponding rhopalia, persists final number mature medusa.