. A text-book of invertebrate morphology. Invertebrates. 84 INVERTEBRATE MORPHOLOGT. 2. Order Narcomedusae. In the HydrarisB the polyp form occurs without a medusa, in the order Narcomedusce the reverse is the case, since in it the medusa form is the only one present in a typical state of development. The medusse are usually somewhat lens- shaped structures (Fig. 42), with a lobed margin, the velum {v), instead of being horizontal, being pendent from the mar-. PiG. 43.—Gunoetaniha oclonaria Haeck. (After Bhooks). TO = margin of bell. ot = otocyst. v — velum. gin (m) and extending up in the int
. A text-book of invertebrate morphology. Invertebrates. 84 INVERTEBRATE MORPHOLOGT. 2. Order Narcomedusae. In the HydrarisB the polyp form occurs without a medusa, in the order Narcomedusce the reverse is the case, since in it the medusa form is the only one present in a typical state of development. The medusse are usually somewhat lens- shaped structures (Fig. 42), with a lobed margin, the velum {v), instead of being horizontal, being pendent from the mar-. PiG. 43.—Gunoetaniha oclonaria Haeck. (After Bhooks). TO = margin of bell. ot = otocyst. v — velum. gin (m) and extending up in the intervals between the lobes. At the apex of each one of these intervals is situated a short, stiff, solid tentacle which is usually bent backward over the exumbrellar surface and is tipped by a knob of nematocysts. The cavity of the short manubrium leads into a gastric chamber which is prolonged out towards the margin into broad pouches which lie opiDosite the tentacles and the intervals be- tween the lobes, and around the margin, following the edge of the lobes and therefore having a festooned arrangement, runs a narrow circular canal which communicates with each radial pouch at the apex of each interlobular interval. This struc- ture is, however, absent in the American species Cunoctantha octonaria. The reproductive organs develop in the subum- brellar ectoderm covering the pouches and sometimes extend on to the manubrium. Around the margin of the lobes are seated club-shaped projecting otocysts {ot) composed of an external layer of ectoderm surrounding a number of endo- dermal cells, one or more of which contain a crystal of carbonate of lime. The ectoderm cells in the neighborhood are largely sensory and provided with long cilia, their inner ends contributing to the formation of the marginal nerve- Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrati
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