128 THE DATA OP 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 hoinologies 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. 



