1889.] NEW-YORK MICROSCOPICAL SOCIETY. 5 



istics. The same impossibility exists as to dividing all organic 

 substances from all inorganic, all classes of vegetables from all 

 other classes, and all groups of similar animals from all other 

 groups of animals. 



These and other like facts compose the foundation of the 

 Evolution Hypothesis of to-day, of which the Lamarckian theory 

 of Descent with Variation is one story, and the Darwinian doc- 

 trine of Natural Selection is another. Perhaps Herbert Spen- 

 cer's extension of the principle of Derivation to the entire 

 range of material things, — to the inorganic and the organic worlds 

 alike, — may be regarded as the pediment and roof, capping and 

 closing over the whole structure. 



Now, every hypothesis is capable of being submitted to a cer- 

 tain order of proof, and modern systems of logic provide us 

 with perfectly trustworthy criteria of the value of such proof. 

 Still, all inductive processes lead ultimately only to varying de- 

 grees of probability. Absolute certainty seems to be an absolute 

 impossibility. Fortunately, however, we are able to support 

 some propositions with such an overwhelming accumulation of 

 evidence that no one can rationally gainsay them. But other 

 affirmations may never be placed beyond the possibility of ques- 

 tion, because anything like sufficient proof of their truth or false- 

 ness is, in the nature of the case, inaccessible. Between these 

 two extremes there is every grade of fact and faith. 



Whether the evolution hypothesis is to any particular mind a 

 rational explanation of the existence and order of the universe 

 or not, depends upon what amount of probability that mind 

 deems necessary as a basis of faith, or what kind of evidence it 

 considers applicable to the matter. Some persons thought the 

 doctrine of derivation was satisfactorily established, as regards 

 organic forms, as soon as it became tolerably clear that it was 

 not absolutely incompatible with any series of known facts in 

 the animal and plant worlds. On the other hand, some insisted 

 that it should be shown to be positively and exclusively conso- 

 nant with every known fact. There are intelligent people who 

 still stand upon this narrow ground. Many scientific men were 

 convinced that Natural Selection was a vera causa applicable to 

 all biological problems, as soon as Darwin set forth what experi- 

 mental verification he had derived from a study of artificial 

 selectiofi. But others proposed further experiments, every one of 

 which seemed to its advocate to be a crucial test. 



