RECENT CKITICISMS AND HYPOTHESES. 567 



affected, its quality also is in some cases affected. Each 

 organ, or at any rate each class of organs, has special nutri- 

 tion — abstracts from the blood a proportion of ingredients 

 different from that abstracted by other organs or classes of 

 organs. Hence may result a deficiency or a surplus of some 

 element: instance the change in the blood which must be 

 caused by growth of a stag's antlers. Now if such effects are 

 always produced, and if, further, a change of general nutri- 

 tion caused by a new food or by a difference of ability to 

 utilize certain components of food, similarly operates (in- 

 stance the above named correlation between horns and wool), 

 then every modification must entail throughout the organism 

 multitudinous alterations of structure. Such alterations 

 will ordinarily be neither in themselves useful nor necessarily 

 correlated with those which are useful ; since they must arise 

 as concomitants of any change, whether adaptive or not. 

 There will consequently arise the innumerable minute differ- 

 ences presented by allied species in addition to the differences 

 called specific. 



On joining with recognition of this general process a recog- 

 nition of the tendency towards localization of deposit, one 

 possible origin of specific marks is suggested. When in an 

 organism the circulating fluids contain useless matter, normal 

 or abnormal, the excretion of it, once determined towards a 

 certain place, continues at that place. Trees furnish examples 

 in the casting out of gums and resins. Animal life yields 

 evidence in gouty concretions and such morbid products as 

 tubercle. A place of enfeebled nutrition is commonly 

 chosen — not unfrequently a place where a local injury has 

 occurred. Xow if we extend this principle, well recognized 

 in pathological processes, to physiological processes, we may 

 infer that where an adaptive modification has so reacted on 

 the blood as to leave some matter to be got rid of, the deposit 

 of this, initiated at some place of least resistance, may pro- 

 duce a local structure which eventually becomes a species- 

 mark. A relevant inquiry suggests itself — What proportion 

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