56 ON THE EDUCATIONAL VALUE n 



no one would have dreamt of questioning the 

 propriety of the deduction, that these creatures 

 have a circulation in one direction ; nor would any 

 one have thought it worth while to verify the 

 point. But, in that year, M. von Hasselt, happen- 

 ing to examine a transparent animal of this class, 

 found, to his infinite surprise, that after the heart 

 had beat a certain number of times, it stopped, 

 and then began beating the opposite way so as 

 to reverse the course of the current, which returned 

 by and by to its original direction. 



I have myself timed the heart of these little 

 animals. I found it as regular as possible in its 

 periods of reversal : and I know no spectacle in 

 the animal kingdom more wonderful than that 

 which it presents all the more wonderful that to 

 this day it remains an unique fact, peculiar to this 

 class among the whole animated world. At the 

 same time I know of no more striking case of the 

 necessity of the verification of even those deduc- 

 tions which seem founded on the widest and 

 safest inductions. 



Such are the methods of Biology methods 

 which are obviously identical with those of all 

 other sciences, and therefore wholly incompetent 

 to form the ground of any distinction between it 

 and them. 1 



1 Save for the pleasure of doing so, I need hardly point out 

 my obligations to Mr. J. S. Mill's System of Logic, in this view 

 of scientific method. 



