Characters, Hereditary and Acquired. 79 



Lastly, not only does it thus appear impossible 

 that during all stages of its development — or while 

 as yet incapable of performing its intricate function — 

 this nascent mechanism can have had any adaptive 

 value ; but even as now fully developed, who will 

 venture to maintain that it presents any selective 

 value? As long as the animal preserves its brain, 

 it will likewise preserve its balance, by the exercise 

 of its intelligent volition. And, if the brain were 

 in some way destroyed, the animal would be 

 unable to breed, or even to feed ; so that natural 

 selection can never have had any opportunity, so 

 to speak, of developing this reflex mechanism in 

 brainless frogs. On the other hand, as we have just 

 seen, we cannot perceive how there can ever have 

 been- any raisott d'etre for its development in normal 

 frogs — even if its development were conceivably 

 possible by means of this agency. But if practice 

 makes perfect in the race, as it does in the individual, 

 we can immediately perceive that the constant habit 

 of correctly adjusting its balance may have gradually 

 developed, in the batrachian organization, this non- 

 necessary reflex ^. 



function. Indeed, a noticeable peculiarity of reflex mechanisms as a class 

 is the highly specialized character of the fnnctions which their highly 

 organized structures subserve. 



' We meet with a closely analogous reflex mechanism in brainless 

 vertebrata of other kinds ; but these do not furnish such good test cases, 

 because the possibility of natural selection cannot be so efficiently 

 attenuated. The perching of brainless birds, for instance, at once refers 

 us to the roosting of sleed^h^rds, where the reflex mechanism 

 concerned is clearly of hiirhjBaCTm value. Therefore such a case is 

 not available as a test, alRughklhe probability is that birds have 

 inherited their balancing mejh^siiffi from their sauropsidian ancestors, 

 where it would have been of iflj sifCh 'adaptive importance. 



