GENESIS, HEREDITY, AND VARIATION. 349 



having its substance everywhere continuously subject to like 

 actions, could undergo none of those changes which life con- 

 sists of; and similarly, an absolutely-uniform species, having 

 all its members exposed to identical influences, would be 

 deprived of that initiator of change which maintains its exist- 

 ence as a species. Just as, in each organism, incident forces 

 constantly produce divergences from the mean state in various 

 directions, which are constantly balanced by opposite diver- 

 gences indirectly produced by other incident forces; and just 

 as the combination of rhythmical functions thus maintained, 

 constitutes the life of the organism; so, in a species, there 

 is, through gamogenesis, a perpetual neutralization of those 

 contrary deviations from the mean state which are caused in 

 its different parts by different sets of incident forces; and it 

 is similarly by the rhythmical production and compensation 

 of these contrary deviations, that the species continues to 

 live. The moving equilibrium in a species, like the moving 

 equilibrium in an individual, would rapidly end in complete 



tained by the unequal and ever-varying actions of incident forces on its dif- 

 ferent parts.' Recent physiological work offers a startling example of the 

 statement." 



To the question contained in the first sentence the answer is that I have 

 not made the statement in the above words, but that it is implied in the chap- 

 ter entitled " The Degree of Life varies as the Degree of Correspondence," and 

 more especially in § 36, which, towards its close, definitely involves the state- 

 ment. The verifying evidence my critic gives me is this : — 



"Prof. Sherrington has shown that if the sensory roots of the spinal nerves 

 are cut one by one there is at first no general effect produced. That is to say, 

 the remainder of the nervous system continues to function as before. This 

 condition (lack of general effect) persists until about six pairs have been cut. 

 With the severance of the seventh pair, however, the whole central nervous 

 system ceases to function, so that stimulation of intact sensory nerves pro- 

 duces no reflex action. After a variable period, but one of many hours dura- 

 tion, the power of functioning is recovered. That is to say, if the sensory 

 impulses (from the skin, &c.) reaching the central nervous system arc rapidly 

 reduced in amount, there comes a point where those remaining do not suffice 

 to keep the structure 'awake.' After a time, however, it adjusts itself to 

 work with the diminished supply. Similarly Strumpell describes the case of 

 a boy * whose sensory inlets were all paralyzed except one eye and one car.' 

 When these were closed he instantly fell asleep." 



