626 



MEDUSAE OF THE WORLD. 



oral tentacles, and then an additional set of tentacles usually develops below the last con- 

 striction. As many as 12 disk-like ephyrae may be cast off one by one, and finally the scypho- 

 stoma is left greatly reduced in size, but still provided with a corona ot tentacles. After all 

 of the ephyrae have been cast off through this terminal budding the scyphostoma frequently 

 develops irregular stolons from its sides and base. Haeckel's observations of other modes 

 of development are discussed in the description of the genus Aurellia. 



The young ephyra has 8 marginal sense-organs flanked by 16 lappets, the ocular clefts 

 of which are only about half as wide and deep as the 8 alternating clefts. The throat is at 

 first a simple 4-cornered tube and the lenticular central stomach gives rise to 16 simple, 

 separate, radiating canals which extend outward in the radii of the tentacles and sense-organs. 

 The tentacles then begin to develop (first one, then others laterally) in the 8 adradial spaces. 

 The lips elongate at the 4 perradial corners and form the mouth-arms, and a peripheral 

 ring-canal is formed by the radial-canals becoming T-shaped at their free, distal ends, and the 

 sides of each adjacent T fusing. As the animal increases in size, blind canals travel centrip- 

 etally inward from the ring-canal even before the ring-canal is complete, and fuse with the 8 

 perradial and interradial canals, which thus become pitchfork-shaped. (See fig. 4, plate 67.) 



Full descriptions and very complete figures of the development of the various stages in 

 Aurellia flavtJula are given by L. Agassiz, 1860-62. Hyde, 1894, gives a detailed and careful 

 account of the development ot the planula and of the early stages of the scyphostoma, and 

 Smith has investigated the process of formation of the gastrula. Clans and Gone, whose 

 views are at variance, studied the development of the scyphostoma and its gastral pouches. 



Macallum, 1903, finds that, in Aurellia flavidula living in brackish water, the salinity 

 of the water may undergo considerable change during the day and yet the amount of NaCl 

 within the body of the Aurellia remain practically constant. The medusa contains slightly 

 less sodium and considerably more potassium than does normal sea-water. It contains 

 also about the same amount of calcium as is found in sea-water, but less magnesium and 32 

 to 36 per cent less SO. He gives the composition of Aurellia, Cyanea and of sea-water as 

 follows: 



27 mature specimens of Aurellia from Tortugas, Florida, all collected at random from a 

 single swarm on May 4, 1906, were of dimensions and proportions as follows: 



Thus individuals among these 27 specimens displayed all of the characteristics of Aurellia 

 aurita, "A. flavidula" "A. tnarginalis," and "A. habanensis" '; and all should be called 

 A. aurita Lamarck, this name being the oldest. I wholly agree with Vanhoffen, 1902, that 

 A. aurita is distributed over all warm and temperate oceans. 



