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THE AMERICAN NATUBALIST 



[You LIU 



three days in % M NaCl, which killed fundulus taken directly 

 from the sea in less than four hours. But in the present case 

 the fundulus from the brackish ponds lived about equally well 

 in pure NaCl solution. The cause of this behavior, which would 

 not be expected from an adaptational standpoint, is believed to 

 lie in the direct effect of the calcium or some other element of 

 the pond water. In % M NaCl solution fundulus from the man- 

 grove creeks and those from a brackish pond lived respectively 

 3.5 and 4.0 hours, roughly, at 20°. The experiments with 1 M 

 NaCl seemed more valuable for the purposes of this inquiry, 

 because of the more rapid toxic etfects, secondary complications 

 being thus more easily avoided. 



V. The fact that the Bermuda fundulus, closely related to F. 

 heterocliius, but living usually in water of greater salinity than 

 that inhabited by the Woods Hole variety, seems also able to 

 withstand a distinctly higher concentration of evaporated sea 

 water than tlie latter will tolerate, is therefore not to be con- 

 sidered an expression of adaptation to life in more saline water. 

 Other members of the same species at Bermuda which are con- 

 tined to brackish ponds of low salinity, and have for at least 

 several generations been restricted to this environment, are 

 equally resistant to concentrated sea water, and to pure NaCl 

 solutions, and more resistant than the fundulus at Woods Hole, 

 indicating that the resistance of the Bermuda form is due to a 

 (lii-ect action of certain constituents of tlie waters in which it 

 lives upon the composition of its surface membranes.* 



1879. Rei>t. Yoy. ClmlU lun r, Z..,.].. Vol. 1, Ft. 6. 

 Loeb, J. 



