. Text-book of zoology for junior students. Zoology. DIVISIONS OF THE IIYDROZOA. 69 special organs, which are developed in the course of the radiating canals of the disc. The resulting enilirj'os are minute free-swimming bodies, covered with cilia, which finally fix themselves, and develop into the plant-like colonies from which the medusoids were derived. Order IV. Medusid/e. Among the most familiar and beautiful of all marine organisnr! are the delicate, transparent, bell-shaped creatures generally known as Jelly-fishes. All the organisms, which are generally spoken of as Jelly-fishes, belon
. Text-book of zoology for junior students. Zoology. DIVISIONS OF THE IIYDROZOA. 69 special organs, which are developed in the course of the radiating canals of the disc. The resulting enilirj'os are minute free-swimming bodies, covered with cilia, which finally fix themselves, and develop into the plant-like colonies from which the medusoids were derived. Order IV. Medusid/e. Among the most familiar and beautiful of all marine organisnr! are the delicate, transparent, bell-shaped creatures generally known as Jelly-fishes. All the organisms, which are generally spoken of as Jelly-fishes, belong to the Hydrozoa, but they difi'er greatly as to their precise nature. The great gelatinous discs which are so frequently cast up on the sea-shore, and which are more especially spoken of in common language as "Jelly-fishes," are mostly the reproductive zooids of a ]jarticular group of Hjidro-oa (the Liwer- narida), and will be subsequently noticed. Less familiar than these, but equally abundant, are certain, usually much smaller, Jelly-fishes which are found floating in the sea near the surface, often in vast numbers, at particular seasons of the year. Many of. Fig. 37. — a A medusiforni ^^onoplioi'e {ThaamaiUias) seen in luulile, sliiiwiii;^' tin; central polypite, tlie radiating and circular canals of tlie disc, the reproductive organs borne in the course of the former, the marginal bodies and tentacles ; 7; The same, viewed from below. The dotted line indicates the margin of the " ; these comparatively minute Jelly-fishes are in reality, as previously noted, neither more nor less than the free-swimming reproductive buds of the Hydroid Zoophytes, or of other groujis of Hydrozoa. That this is their true nature is shown by the fact that the eggs which they produce develop themselves not into fresh Mediisd', but into various other forms of Uydrnzoit., which may l>e either fixed or oceanic. On the other hand, there are certain Jelly-fishes (Traidiy
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1885
