. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. I02 MANUAL OK ZOOLOGY. simple, or it may be produced into lobes, which are most frequently four in number. The essential elements of genera- tion are produced in simple expansions either of the wall ol the manubrium cr of the radiatmg nectocalycine Fig. 22.—Group of naked-eyed Medusis. A Sarsia gemmifera, with meduso'.ds arising: froni the sides of the central polypite (after Greene); B Madceria formosa (after Forjaes); C /'(7/j'jr^«:Vz ^/(/^n (after Gosse). From the abo
. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. I02 MANUAL OK ZOOLOGY. simple, or it may be produced into lobes, which are most frequently four in number. The essential elements of genera- tion are produced in simple expansions either of the wall ol the manubrium cr of the radiatmg nectocalycine Fig. 22.—Group of naked-eyed Medusis. A Sarsia gemmifera, with meduso'.ds arising: froni the sides of the central polypite (after Greene); B Madceria formosa (after Forjaes); C /'(7/j'jr^«:Vz ^/(/^n (after Gosse). From the above description it will be evident that the Medusa is in all essential respects identical in structure with the free-swimming generative biid or gonophore of many of the fixed and oceanic Hydrozoa. Indeed, a great many forms which were previously included in the Medusidcs have now been proved to be really of this nature, and it may fairly be doubted if this will not ultimately be found to apply to all. As to the value, however, of the order Medusidce, the present state of our knowledge is well expressed by the following con- clusions which have been drawn up by Professor Greene :— " I. That several of the organisms formerly described as MedusidcB are the free gatiophores of other orders of Hydrozoa. " 2. That the homology of these free gonophores with those simple expansions of the body-wall which in Hydra and some other genera are known to be reproductive organs by their contents alone, is proved alike by the existence of numerous transitional forms and by an appeal to the phenomena of their Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Nicholson, Henry Alleyne, 1844-1899. New York : D. Appleton
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