426 



MEDUSAE OF THE WORLD. 



Gonads usually rose-pink, but occasionally dull yellowish-white or colorless. Stomach and 

 entodermal cores of tentacles usually pink, but occasionally dull-white or colorless. 



This medusa is widely distributed, being found in the tropical parts of the Atlantic, 

 Pacific, and Indian Oceans, and in the Mediterranean. It is not seen in impure harbors, 

 but is a creature of the surface of the open sea far from coasts, being independent of land for 

 its developmental stages. 



The development has been studied in detail by Fol, 1873, and Metschnikoff, 1886. 

 The egg is o. 23 to 0.33 mm. in diameter and is laid at mid-day during April in the Mediterra- 

 nean. The segmentation is total and equal, and the entoderm is formed by delamination from 

 the inner ends of the cells of the blastula at the 16-cell stage. The details of development are, 



282. 



Fig. 282. — Geryonia proboscidalis, mature medusa, showing muscular system. From life, by the author, 



Zoological Station, Naples, December 3, 1907. 

 Fig. 283. — Geryonia "elephas," after Haeckel, in Syst. der Medusen. 



indeed, quite similar to those of Liriope, excepting that there are 6 primary tentacles instead 

 of 4, as in Liriope, and there are also 6 interradial fusions of the walls of the primary stomach- 

 cavity. (See text-fig. 267.) 



This medusa is far more abundant and grows to a greater size in the Mediterranean 

 than in other parts of the world. Specimens from Florida and the Bahamas are nearly always 

 pink in color, whereas the Mediterranean medusae are colorless, milky, or brownish-yellow. 

 One rarely sees the American medusa more than 50 mm. in diameter, whereas in the Mediter- 

 ranean specimens 75 mm. wide are abundant. 



Bethe, 1903, 08, 09, finds that if the medusa be paralyzed by removal of its bell-margin, 

 NaCl is a local stimulant and will revive temporary pulsations. On the other hand Mg 

 inhibits pulsation. The medusa displays a refractory period similar to that observed by 

 Marey, 1876, in the vertebrate heart. It can not be stimulated when in systole at normal 

 temperatures. The effects of the ions of the salts of sea-water are essentially the same in both 

 Geryonia and Rhizostoma. 



