,8^ THE EVOLUTION OF FLAT-FISH. 359 



1 consider necessary the introduction of assumptions indicating to 

 biologists in what sense they should direct their observations or their 

 experiments, and which may suggest these experiments. I have 

 long since expressed my opinion on those naturalists who have not 

 sufficient imagination to createfor themselves assumptions, or enough 

 courage to give vent to them. We must run the risk of making 

 mistakes sometimes, and be always ready to abandon a theory which 

 is proved incorrect. 



But before discussing with Mr. Cunningham the explanation 

 that I have given of the asymmetry of the Pleuronectids, and 

 which has been accepted by so competent a zoologist as Professor A. 

 Agassiz, I shall wait till my contradictor has brought me conclusive 

 experiments, or new observations, and not merely sterile and 

 destructive criticism. 



A. GlARD. 



