. A manual of zoology. Zoology. II. SCYPHOZOA: 223 septa of the scyphostoma (p. 220). Since the ephync differ markedly from the adult medusce and only gradually change into the sexual form, the alternation of generations is complicated by a metamorphosis. This metamorphosis persists in some cases (Pelagia noctibtca) where the alter- nation of generations is suppressed; the egg develops directly into an ephyra, which transforms into the adult Fig. 188.—Development of Aurelia aurita (from Hatschek). First row, growth of planula to scyphostoma; below, strobilation (separ
. A manual of zoology. Zoology. II. SCYPHOZOA: 223 septa of the scyphostoma (p. 220). Since the ephync differ markedly from the adult medusce and only gradually change into the sexual form, the alternation of generations is complicated by a metamorphosis. This metamorphosis persists in some cases (Pelagia noctibtca) where the alter- nation of generations is suppressed; the egg develops directly into an ephyra, which transforms into the adult Fig. 188.—Development of Aurelia aurita (from Hatschek). First row, growth of planula to scyphostoma; below, strobilation (separation of ): left, oral view of scyphostoma; right, two ephyrse. Order I. Discomedusae. The foregoing account applies, as a whole to only the Discomedusce, the widest distributed and most abundant of the Scyphomedusae. The order is divided into two suborders, I. , mouth X-shaped with long fringed and very mobile arms at the corners of the mouth. Aurelia flavidula* and Cyanea arctica* common in north Atlantic waters, the latter large, exceptionally seven feet in diameter; Pelagia* Ulmaris (fig. 186). (2) ;, four oral arms which branch dichotomously; the mouth and grooves on the arms closed by union of their edges so that many small slomata remain through which food is taken. Stomolophus* Polyclonia'^ (fig. 187). Certain Scyphomedusa; are distinguished from the Discomedusae. Some of these are inhabitants of the deep seas and only recendy known; others differ so from the Discomedusae that the relationship was not seen at first. These have in common the cathainma, four partitions, homologous to the tEeniote of the scyphostoma, which bear the phacelte and divide the peripheral part of the gastral cavity in such a way that the gonads are separated into eight groups. The marginal bodies vary in three Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appear
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
