STRATIFICATION IN TIME. 33 



in comparing the organs of the individual, their action and 

 their distribution, with the different species of animal, and 

 their present distribution and functions on the globe. The 

 fauna of a district thus takes the aspect of a vast organism 

 whose separate members -the different species of animals are 

 living parts of the body, and which has had too its embryology, 

 i.e. its development in time. These species, as regards the 

 laws of their local distribution, may be regarded morphologically 

 as the limbs of a gigantic organism which throws one or another 

 of them up into the air on to the top of some mountain peak, 

 while others are flung into ocean depths, subterranean caves, 

 lakes, or rivers. But they may also be studied physiologically, 

 and compared to organs which by their functions and import- 

 ance influence the life of the whole mass, and are interdepen- 

 dent by the most various physiological relations, like the organs 

 of a healthy living organism. 



It is in agreement with taese arguments that we apply 

 the expression ' Universal Physiology,' or ' the Physiology of 

 Organisms' in contradistinction to the Physiology of Organs, 

 to that branch of animal biology which regards the species 

 of animals as actualities and investigates the reciprocal rela- 

 tions which adjust the balance between the existence of any 

 species and the natural, external conditions of its existence, 

 in the widest sense of the term. Each separate organ, even 

 when influenced by other parts of the body, must exercis? its 

 own specific function. The sum, or, to speak more accurately, 

 the resultant, of all the forces simultaneously at work in an 

 individual, constitutes its individual life : and its general well- 

 being and its capability for maintaining the place it has once 

 acquired in the struggle for existence are the result of a 

 combination of the numerous different and often antagonistic 

 functions of the individual organs. This is equally true of 

 species, if we regard them as members of a single vast organ- 

 ism ; and this organism can only maintain its place in existence 

 the distribution, that is, of its members on the surface of the 

 earth by the efficient action of its functions, i.e. by the reci- 

 procal activity of the species which constitute it, sometimes 



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