CHANGES IN SALINITY AND THEIR EFFECTS UPON THE REGENERA- 

 TION OF CASSIOPEA XAMACHANA. 



By a. J. GOLDFARB. 



Cassiopea xamachana, a large scyphomedusa, is very abundant in the 

 very shallow waters of the moat at Fort Jefferson, Dry Tortugas, Florida. 

 The conditions in this moat are such that the medusae are in all probability 

 subjected to extreme changes in salinity, due on the one hand to evaporation 

 in the subtropical sun, to the shallow water and inclosed nature of the moat, 

 to the single tide, etc., and on the other hand to extreme dilution due to the 

 subtropical rains. Doctors A. G. Mayer and T. W. Vaughan have under- 

 taken a study of these changes in salinity in and outside of the moat, under 

 various conditions of tide and season. Until their report is forthcoming, 

 this phase of the problem must be left in abeyance. 



The present report considers to what extent changes in salinity influence 

 regeneration in Cassiopea, and the results of the investigation are compared 

 with those previously obtained with the hydroid Eiidendriiim ramosum of 

 Woods Hole, Massachusetts, and with the observations of Loeb with the 

 hydroid Tuhularia of Serino Bay, Italy. 



Though certain variable factors are known to accelerate, retard, or 

 modify the regeneration of an organism, these factors have not heretofore 

 been sufficiently taken into account. In the present investigation much 

 care was taken to exclude or make the following factors uniform : 



1. Size of medusce. Size roughly indicates age, and as the rate of growth 

 varies with age the medusae finally chosen were approximately of the same 

 size. Each solution contained one of medium size, lOO to 105 mm. in 

 diameter, and one smaller medusa, 85 to 90 mm. in diameter. 



2. Volume, surface, and depth of solution. To insure uniformity of respira- 

 tion and evaporation, and to prevent excessive concentration, the medusae 

 were kept in jars of equal size and shape, each jar containing 2,000 c.c. of the 

 solution. 



3. Aeration and change of solution. All solutions were shaken thoroughly 

 to aerate them, and were changed daily to avoid excess CO2, excess evapora- 

 tion, and bacteria. 



4. Degree of injury. It has been repeatedly urged that the rate of regen- 

 eration is influenced by the extent of injury. Though recent evidence is 

 opposed to this view, its possibility was taken into account by removing the 

 same number of arms from each pair of medusae. 



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