Changes in Salinity and Effects on Regeneration^ etc. 93 



series of densities, for the increased density of the sea-water at the Dry 

 Tortugas is paralleled by each of the changes already cited in table 6; but 

 when Tuhularia of Serino Bay, whose density is 3.83, is taken into consider- 

 ation, no correlation between density and the character of the curve obtains, 

 except in two particulars: (i) the greater the density of the sea, the greater 

 the dilution in which regeneration will take place ; (2) the greater the density 

 of the sea the greater the regeneration in the hypotonic solutions, i. e., 

 Eudendrium A 3.29, maximum regeneration is 35 per cent above norm 

 Cassiopea, A 3.54, 60 per cent, Tuhularia, A 3.83, 120 per cent. 



Subject to a more accurate analysis of the density of the water in the 

 moat at Fort Jefiferson and at Serino Bay, these conclusions must be con- 

 sidered tentative only. The fact remains, however, that Loeb's limited 

 data are not in accord with the results obtained in two different organisms 

 from two different localities whose sea-water was of different densities. 

 It is also clear that the more detailed and more numerous data upon Euden- 

 drium and Cassiopea are in close agreement. And we are driven to the 

 conclusion that either Tuhularia, for some inexplicable reason, differs in 

 its behavior from the other two coelenterates, a view which is very im- 

 probable, or that the insufficient data upon Tuhularia has misled the author. 

 The close similarity of Eudendrium and Cassiopea and the corroborative 

 results of A. G. Mayer upon the effects of changes in density upon nerve- 

 conduction leads me to believe that the results here given may be taken as 

 indicative of the gross effects, without any effort to segregate the osmotic 

 from the ionic influences, upon the regeneration of these organisms. 



SUMMARY. 



The object of this investigation was to ascertain to what extent changes 

 in salinity affected an organism, Cassiopea xamachana, normally subject to 

 relatively great variation in the concentration of the sea-water, and to 

 compare the results with those of the hydroid Eudendrium and the hydroid 

 Tuhularia. 



Considerable attention was paid to render the following variable factors 

 uniform for the series: Size of medusae; volume, surface, and depth of the 

 solutions; extent of injury; level of amputation; temperature; crowding. 



Injurious or other variable factors were guarded against: (i) by aerating 

 and changing all solutions daily; (2) by diluting with water containing 

 known amount of sea-salts; (3) by concentrating the sea-water very slowly; 

 (4) by examining the 323 regenerating arms at intervals of 14, 24, and 30 

 days. 



Cassiopea lived in solutions ranging from 40 to 153 per cent sea-water 

 solutions. 



Regeneration occurred in solutions containing 50 to 133 per cent sea- 

 water. 



Normal regeneration of the arms occurred within much narrower range, 

 namely, 75 to 105 per cent. Beyond these limits regeneration was atypic. 



