IMPRESSIBILITY OF ORGANISMS. 307 



are merely asked to point out a conceivoMe mode. On the 

 other hand, they ask, not simply for a conceivable mode, 

 but for the actual mode. They do not say — Show ns how 

 this may take place ; but they say — Show us how this does 

 take place. So far from its being unreasonable to put the 

 above question, it would be reasonable to ask not only for 

 2k possible mode of special creation, but for an ascertained 

 mode ; seeing that this is no greater a demand than they 

 make upon their opponents. 



And here we may perceive how much more defensible 

 the new doctrine is than the old one. Even could the sup- 

 porters of the Development Hypothesis merely show that 

 the origination of species by the process of modification is 

 conceivable, they would be in a better position than their 

 opi^onents. But they can do much more than this. They 

 can show that the process of modification has effected, and 

 is effecting, decided changes in all organisms subject to 

 modifying influences. Though, from the impossibility of 

 getting at a sufficiency of facts, they are unable to trace 

 the many phases through which any existing species has 

 passed in arriving at its present form, or to identify the in- 

 fluences which caused the successive modifications ; yet, 

 they can show that any existing species — animal or vegeta- 

 ble — when placed under conditions different from its pre- 

 vious ones, immediately begins to undergo certaih changes 

 of structure fitting it for the new conditions. They can 

 show that in successive generations these changes continue, 

 until ultimately the new conditions become the natural 

 ones. They can show that in cultivated plants, in domesti- 

 cated animals, and in the several races of men, such altera- 

 tions have taken place. They can show that the degrees 

 of difference so produced are often, as in dogs, greater than 

 those on which distinctions of species are in other cases 

 founded. They can show that it is a matter of dispute 

 wb*^ther some of these modified forms are varieties or sepa- 



