THE FACTORS OF ORGANIC EVOLUTION. 769 



performed by them have to constitute a moving equilibrium ; and the 

 function of one cannot, by alteration of the structure performing it, 

 be modified in degree or kind, without modifying the functions of the 

 rest — some appreciably and others inappreciably, according to the 

 directness or indirectness of their relations. Of such inter-dependent 

 changes, the normal ones are naturally inconspicuous ; but those which 

 are partially or completely abnormal, sufficiently carry home the gen- 

 eral truth. Thus, unusual cerebral excitement affects the excretion 

 through the kidneys in quantity or quality or both. Strong emotions 

 of disagreeable kinds check or arrest the flow of bile. A considerable 

 obstacle to the circulation offered by some important structure in a 

 diseased or disordered state, throwing more strain upon the heart, 

 causes hypertrophy of its muscular walls ; and this change which is, 

 60 far as concerns the primary evil, a remedial one, often entails mis- 

 chiefs in other organs. "Apoplexy and palsy, in a scarcely credible 

 number of cases, are directly dependent on hypertropic enlargement 

 of the heart." And in other cases, asthma, dropsy, and epilepsy are 

 caused. Now if a result of this inter-dependence as seen in the indi- 

 vidual organism, is that a local modification of one part produces, by 

 changing their functions, correlative modifications of other parts, then 

 the question here to be put is — Are these correlative modifications, 

 when of a kind falling within normal limits, inheritable or not ? If 

 they are inheritable, then the fact stated by Mr. Darwin that " when 

 one part is modified through continued selection," " other parts of the 

 organization will be unavoidably modified " is perfectly intelligible : 

 these entailed secondary modifications are transmitted /^a^v'^jiassM with 

 the successive modifications produced by selection. But what if they 

 are not inheritable ? Then these secondary modifications caused in 

 the individual, not being transmitted to descendants, the descendants 

 must commence life with organizations out of balance, and with each 

 increment of change in the part affected by selection, their organiza- 

 tions must get more out of balance — must have larger and larger 

 amounts of re-organization to be made during their lives. Hence the 

 constitution of the variety must become more and more unworkable. 



The only imaginable alternative is that the re-adjustments are 

 effected in course of time by natural selection. But, in the first place, 

 as we find no proof of concomitant variation among directly co-opera- 

 tive parts which are closely united, there cannot be assumed any con- 

 comitant variation among parts which are both indirectly co-operative 

 and far from one another. And, in the second place, before all the 

 many required re-adjustments could be made, the variety would die 

 out from defective constitution. Even were there no such difficulty, 

 we should still have to entertain a strange group of propositions, which 

 would stand as follows : 1. Change in one part entails, by reaction 

 on the organism, changes, in other parts, the functions of which are 

 necessarily changed. 2. Such changes worked in the individual, affect, 

 VOL. xxviii. — 49 



