Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 23& Ihe muscular epithelium and the jabrous layer. The ganglion cells in the upper nerve-ring are smaller, and the fibrillar given off from it pass to the tentacles. The fibrillar of the sense nerves may be derived from both rings. The marginal bodies have long been recognised as sense organs, and are either eye spots (ocelli) or auditory vesicles; hence the Hydromedusoi may be divided into two groups, the Ocellata or Vesiculata. In the Vesiculata the auditory vesicles ar
Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 23& Ihe muscular epithelium and the jabrous layer. The ganglion cells in the upper nerve-ring are smaller, and the fibrillar given off from it pass to the tentacles. The fibrillar of the sense nerves may be derived from both rings. The marginal bodies have long been recognised as sense organs, and are either eye spots (ocelli) or auditory vesicles; hence the Hydromedusoi may be divided into two groups, the Ocellata or Vesiculata. In the Vesiculata the auditory vesicles are situated at the edge of the under side of the umbrella, and contain one or more concretions (otoliths)^\hic]i-Ave formed in the interior of cells. Peculiar sense cells surround each vesicle-like cell containing a concretion. The curved hairs of these sense cells (auditory hairs) are in contact with the con- cretion vesicle, A nerve tibrilla enters the basis of the auditory S3). The audi- tory organs of the Tra- clii/mediosce are placed above the velum, and are in con- nection with the upper nerve ling; they have the form of small projecting tentacles furnislied with otoliths and auditoiy hairs. The tentacle may either project freely on the surface {Trachijnema), or, as in Geryonia, it may be placed in a vesicle (fig, 184) which lies in the gelatinous substance of the disc and close to the edge of the latter. Sepai-ate sexes are almost invariably the rule, but it is rare to find that the colonies are dioecious, , that male and female medusoids are developed in different colonies [Tubularia). Gemma- tion has occasionally been observed among the Medusoi {Sarsia j)roKfera) and division [StomohracJiium mirablle). The larvse of Cunina, which are parasitic on the Genjonidai, may also there give rise to a cluster of Duas, Fig. 183.—Sens I ou the nerve-ring and circular vessel of Octorchi) (after O. and E. Hertwig). Rh, Sense organ ; O, O', two otoliths; Hh, audi- tory cilia ; H
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