CHAPTER XI. 



INTERPRETATION AND QUALIFICATION. 



362. CONSIDERING the difficulties of inductive verifica- 

 tion, we have, I think, as clear a correspondence between the 

 a priori and a posteriori conclusions, as can be expected. The 

 many factors co-operating to bring about the result in every 

 case, are so variable in their absolute and relative amounts, 

 that we can rarely disentangle the effect of each one, and 

 have usually to be content with qualified inferences. Though 

 in the mass organisms show us an unmistakable relation 

 between great size and small fertility, yet special compari- 

 sons among them are nearly always partially vitiated by 

 differences of structure, differences of nutrition, differences of 

 expenditure. Though it is beyond question that the more 

 complex organisms are the less prolific, yet as complexity 

 has a certain general connexion with bulk, and in animals 

 with expenditure, we cannot often identify its results as inde- 

 pendent of these. And, similarly, though the creatures which 

 waste much matter in producing motion, sensible and insen- 

 sible, have lower rates of multiplication than those which 

 waste less, yet, as the creatures which waste much are 

 generally larger and more complex, we are again met by an 

 obstacle which limits our comparisons, and compels us to 

 accept conclusions less definite than are desirable. 



Such difficulties arise, however, only when we endeavour, 

 as in foregoing chapters, to prove the inverse variation 

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