Medusae of the world . dusais brick-red (plate 35, fig. 6). In most individuals, however, the colored granules are so faintas to be almost imperceptible. In some specimens there is a more or less decided green spotin the entoderm of each tentacle-bulb. This medusa was exceedingly abundant at Tortugas, Florida, from June to August,1897 to 1904. In 1905 it was relatively rare, and only 3 specimens were seen throughout thesummers of 1906 and 1907 although extensive search was made daily with the tow-net, andnot a single specimen could be found in 1908. At times during July, 1898, these medusa?wer
Medusae of the world . dusais brick-red (plate 35, fig. 6). In most individuals, however, the colored granules are so faintas to be almost imperceptible. In some specimens there is a more or less decided green spotin the entoderm of each tentacle-bulb. This medusa was exceedingly abundant at Tortugas, Florida, from June to August,1897 to 1904. In 1905 it was relatively rare, and only 3 specimens were seen throughout thesummers of 1906 and 1907 although extensive search was made daily with the tow-net, andnot a single specimen could be found in 1908. At times during July, 1898, these medusa?were so abundant upon the surface that one could not dip up a bucketful of water withoutcapturing several specimens. In 1909 it again appeared in fair numbers. This is the only pentamerous Hydromedusa known, and it has apparently arisen as a self-perpetuating sport, or mutation, from some species of Clytia or Phtalidium. Indeed themedusa bears a close superficial resemblance to Clytia folleata McCrady, which is also abun-. LEPTOMEDUSiE PSEUDOCLYTIA, GASTROBLASTA. 279 dant at Tortugas. It may be distinguished, however, by its color and the position of itsgonads upon the radial-canals, so that abnormal 4-rayed specimens of P. pentata can be dis-tinguished from the normal Clytia folleata. Believing that P. pentata may be a successful mutation from some Clytia, in 1899 I carriedout a study of the variations of 1,000 specimens. The following is a summary of the results:Among 1,000 specimens of P. pentata, 703 were normal and had 5 radial-canals and 5 lips, 720apart, while 297 were abnormal. Of the abnormal medusae 151, or fully half, were radiallysymmetrical. Medusae which are not radially symmetrical are very apt to be bilaterallysymmetrical. Normal 5-rayed medusae are more apt to be fertile and produce more ova thando abnormal medusae, and thus the abnormal forms are produced at a disadvantage. Thecommonest aberration is to display 4 radial-canals or 4 lips, or both, thus apparently
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcnidari, bookyear1910
