EFFECTS OF STARVATION, AND OF DECREASED SALINITY. 17 



Medusa. The greenish color of the oral filaments disappears, and the 

 plant cells become shriveled and densely crowded. A Medusa starved 

 in light is more active and shrinks more rapidly than does one starved 

 in darkness, and thus it appears that metabolism proceeds more rap- 

 idly in light than in darkness. For example, a Medusa starved in 

 diffused daylight had a diameter at the beginning of the experiment 

 of 78 mm. At the end of 2 months its diameter was 37 mm., and at 

 the end of 3 months, 21 mm., being still vigorous and pulsating at the 

 rate of 16 per minute. 



These starved Medusae exhibited certain phenomena of degenera- 

 tion. The mouth-arms became reduced to mere stumps, most of the 

 mouths closed over, and the oral tentacles and filaments were absorbed 

 or cast off, so that the oral surfaces of the mouth-arms became quite 

 smooth and rounded. The marginal lappets of the disk became 

 blunted, and the dull-white peripheral ring of the ex-umbrella was 

 much reduced in width. Only immature eggs were found in the 

 gonads of starving Medusae. It appears remarkable that the first 

 parts to degenerate are the mouths and mouth-arms, although these 

 are the most important to the organism if in danger of starvation. 

 The marginal sense-organs remained normal in size and appearance. 



Cassiopea xamachana lives in salt-water lagoons having but limited 

 communication with the sea, and it is therefore not surprising that it 

 will survive considerable alterations of salinity. Fresh water (rain- 

 water) is quickly fatal to the Medusae, for they shrivel rapidly; all 

 pulsations cease, and even if removed to salt water after less than five 

 minutes' exposure to the fresh, recovery is very slow. On the other 

 hand , if every night and morning we decrease the salt and increase 

 the fresh water 5 per cent, the Medusae can be brought into a mixture 

 of 25 per cent sea -water plus 75 per cent fresh water, and still sur- 

 vive. Their rates of pulsation become successively slower as the salt 

 water is reduced. 



Thus, two Medusae in pure sea- water had rates of pulsation of 20 and 

 60, respectively ; in 60 per cent sea-water plus 40 percent fresh water, 

 1 8 and 1 8 , respectively ; in 50 per cent sea-water plus 50 per cent fresh 

 water, 14 and 18, respectively; in 40 per cent sea- water plus 60 per 

 cent fresh water, 8 and 4, respectively; in 35 per cent sea-water plus 

 65 per cent fresh water, 7 and 2, respectively; in 30 percent sea-water 

 plus 70 per cent fresh water, 3 and 2, respectively; in 25 per cent sea- 

 water plus 75 per cent fresh water, 3. 



The small Medusa ceased to pulsate in 75 per cent fresh plus 25 per 

 cent sea -water, and its sub-umbrella surface became insensitive to the 

 most powerful stimuli, such as a touch of a crystal of KC1 or K SO 4 ; 

 yet when transferred to 50 per cent fresh plus 50 per cent sea water it 



