COKEELATION. 57 



Correlation of Organs. 

 § 48. 



The changes in the organism which are due to differentiation 

 and reduction are the cause of a fresh series of phenomena in the 

 factors which gave rise to them. From the conception that life is 

 the harmonious expression of a collection of phenomena regularly 

 conditioned, it follows that the activity of an organ cannot be 

 regarded as really existing for itself alone. 



Every kind of arrangement presupposes a series of other arrange- 

 ments ; every organ, therefore, must have intimate relations with 

 the rest, and be more or less dependent on others. Every move- 

 ment in a muscle presupposes the existence of a nerve ; and both 

 of these organs presuppose the existence of a nutrient system. 

 In this way one function has an intimate connection with other 

 apparently dissimilar functions. This relation, which was first defi- 

 nitely pointed out by Cuvier, and which is known as Correlation, 

 shows us the road by which we can attain to a correct appreciation 

 of animal organisation. By far the most important point is the 

 conception of the organism as an individual whole, which is as much 

 conditioned by its parts, as one part is conditioned by others. 

 Correlation is a necessary result of this conception. 



Not only the general arrangements of the organisation, but also 

 its apparently more subordinate features, exhibit intimate relations 

 with one another, and a change which affects one system of organs, 

 simultaneously produces modifications in some of the other organs. 

 These are adaptations to changes, which themselves are due to 

 adaptations. They are, however*, of a secondary character, while 

 those which are of a primary character have their origin in the 

 outer world. 



Correlation may be divided into the more and the less remote ; 

 where less remote it is expressed in one system of organs or in 

 other systems functionally connected with this ; when more 

 remote, in organs which are functionally less related to it. Physio- 

 logical principles are essential in the investigation of correlation, 

 and it is necessary, therefore, to know what are the functions of 

 separate organs, or at least what their value is in the animal 

 economy, in order to be able to recognise it. So, too, it is of im- 

 portance to know what are the habits of the animal, for the original 

 forces, on which the various relations of the organs depend, are due 

 to them. 



As the forces which cause changes in the organism either lie 

 without the organism, or, as most of them, are to be sought for 

 without it, they do not come within the scope of our work. Com- 

 parative Anatomy, therefore, is limited all round by a wide but 

 uncultivated region, in which rich harvests may be gathered for 

 biological science, whenever its treatment is taken in hand. 



