THE SCOPE OF BIOLOGY. 129 



Here, however, as before, comparison of special truths, 

 besides facilitating their interpretation, brings to light certain 

 general truths. Contrasting functions bodily and mental as 

 exhibited in various kinds of organisms, shows that there 

 exists, more or less extensively, a community of processes 

 and methods. Hence result two groups of propositions con- 

 stituting General Physiology and General Psychology. 



§ 40. In these divisions and subdivisions of the first two 

 great departments of Biology, facts of Structure are con- 

 sidered separately from facts of Function, so far as separate 

 treatment of them is possible. The third great department 

 of Biology deals with them in their necessary connexions. 

 It comprehends the determination of functions by structures, 

 and the determination of structures by functions. 



As displayed in individual organisms, the effects of struc- 

 tures on functions are to be studied, not only in the broad 

 fact that the general kind of life an organism leads is neces- 

 sitated by the main characters of its organization, but in the 

 more special and less conspicuous fact, that between mem- 

 bers of the same species, nmior differences of structure lead 

 to minor differences of power to perform certain actions, and 

 of tendencies to perform such actions. Conversely, 



under the reactions of functions on structures in individual 

 organisms, come the facts showing that functions, when ful- 

 filled to their normal extents, maintain integrity of structure 

 in their respective organs; and that within certain limits 

 increases of functions are followed by such structural changes 

 in their respective organs, as enable them to discharge better 

 their extra functions. 



Inquiry into the influence of structure on function as seen 

 in successions of organisms, introduces us to such phenomena 

 as Mr. Darwin's Origin of Species deals with. In this cate- 

 gory come all proofs of the general truth, that when an in- 

 dividual is enabled by a certain structural peculiarity to per- 

 form better than others of its species some advantageous 



