128 THE DATA OF BIOLOGY. 



as a separate study. And since it would be very incon- 

 venient wholly to dissociate Objective Psychology from Sub- 

 jective Psychology, we are practically compelled to deal with 

 the two as forming an independent science. 



Obviously, the functional phenomena presented in succes- 

 sions of organisms, similarly divide into physiological and 

 psychological. Under the physiological come the 



modifications of bodily actions that arise in the course of 

 generations, as concomitants of structural modifications ; and 

 these may be modifications, qualitative or quantitative, in 

 the molecular changes classed as chemical, or in the organic 

 actions classed as physical, or in both. Under the 



psychological come the qualitative and quantitative modifica- 

 tions of instincts, feelings, conceptions, and mental processes 

 in general, which occur in creatures having more or less 

 intelligence, when certain of their conditions are changed. 

 This, like the preceding department of Psychology, has in 

 the abstract two different aspects the objective and the sub- 

 jective. Practically, however, the objective, which deals with 

 these mental modifications as exhibited in the changing 

 habits and abilities of successive generations of creatures, is 

 the only one admitting of investigation; since the corre- 

 sponding alterations in consciousness cannot be immediately 

 known to any but the subjects of them. Evidently, con- 

 venience requires us to join this part of Psychology along 

 with the other parts as components of a distinct sub-science. 



Light is thrown on functions, as well as on structures, by 

 comparing organisms of different kinds. Comparative Phy- 

 siology and Comparative Psychology, are the names given to 

 those collections of facts respecting the homologies and 

 analogies, bodily and mental, disclosed by this kind of in- 

 quiry. These classified observations concerning likenesses 

 and differences of functions, are helpers to interpret func- 

 tions in their essential natures and relations. Hence Com- 

 parative Physiology and Comparative Psychology are names 

 of methods rather than names of true subdivisions of Biology. 



