312 On Species, 



3. Variations of S2:>ec{es. 



But there are variations in specieSj and this is our next topic. 

 The principles already considered teach, as we believe, that each 

 species has its specific value as a unit, which is essentially per- 

 manent or indestructible by any natural source of change ; and 

 we have, therefore, to admit in the outset, if these principles are 

 true, that variations have their limits, and cannot extend to the 

 obHte ration of the fundamental characteristics of a species. 



To understand these variations, we may again appeal to gen- 

 eral truths. 



Yariation is a characteristic of all things finite ; and is involved 

 in the very conditions of existence. No substance or body can 

 be wholly independent of every or any other body in the uni- 

 verse. The most comprehensive and influential law in nature, 

 most fundamental in all change, composition or decomposition, 

 growth or decay, is the law of mutual sympathy, or tendency to 

 equilibrium in force through univers^ action and reaction. 



The planets have their orbits modified by other bodies in space 

 throu<>;h their chann-ing relations to those bodies. A substance, 



^_ ...^.^ ^..V.V..Q...Q 



as oxygen or iron, varies in temperature and state of expansion 

 from the presence of a body of different temperature; in chem- 

 ical tendencies from the presence of a luminous body like the 

 sun; in magnetic or electrical attraction from surrounding mag- 

 netic or electrical influences. There is thus unceasing flow and 

 uncea^inpr change through the universe. All the natural forces 

 are closely related as if a common family or group, and are m 

 constant mutual interplay. 



The degree or kind of variation has its specific law for each 

 element ; and in this law the specific nature of the element is m 

 a degree expressed. There is to each body or species, the nor- 

 mal or fundamental force in which its very nature consists; and, 

 in addition, the relations of this force to other bodies, or kinds, 

 amounts or conditions of force, upon which its variations depend. 

 One great end of inorganic science is to study out the law of 

 variables for each element or species. For this law is as much a 

 part of an idea of the species, as the fundamental potentiality; 

 indeed the one is a measure of the other. 



^ So again, a species in the organic kingdoms is subject to vana- 

 tions, and upon the same principle. Its very development de- 

 pends on the appropriation of material around it, and on attend- 

 ing physical forces or conditions, all of which are variable 

 through the whole of its history. Every chemical or molecular 

 law m the universe is concerned in the growth,-— the laws ot 

 teat, light, electricity, cohesion, etc. ; and the progress of the 

 developing germ, whatever its primal potentiality, is unavoid- 

 ably subject to variations, from the diversified influences to 

 which it may be exposed. The new germ, moreover, takes 



^^ 



