86 LAY SERMONS, ADDRESSES, AND REVIEWS. [v. 



thought it worth while to verify the point. But, in that 

 year, M. von Hasselt, happening 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 kuow 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 



But I shall be asked at once, Do you mean to say 

 that there is no difference between the habit of mind 

 of a mathematician and that of a naturalist % Do you 

 imagine that Laplace might have been put into the 

 Jardin des Plantes, and Cuvier into the Observatory, 

 with equal advantage to the progress of the sciences 

 they professed ? 



To which I would reply, that nothing could be further 

 from my thoughts. But different habits and various 

 special tendencies of two sciences do not imply different 

 methods. The mountaineer and the man of the plains 

 have very different habits of progression, and each 



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. 



