THEISM AND B VOL UTION. 31 5 



envisaged under three different aspects, to wit : the 

 metaphysical, the logical, and the physiological or 

 real. As to the metaphysical and logical aspects, 

 both the Angelic Doctor and the School gener- 

 ally, are one in attributing to species an absolute 

 fixity. 1 



With metaphysical and logical species, however, 

 we are not at present concerned. I am quite willing 

 to leave these to the metaphysician to treat them 

 as he lists. The question now at issue regards only 

 physiological species. Is the species of which the 

 biologist speaks variable, or does it belong to the 

 category of immutable metaphysical species ? This 

 is a question of science and not of metaphysics. If 

 it can be proven by the sciences of observation and 

 experiment, that species are permanent and in- 

 variable, then the real or physiological species of 

 the naturalist, in so far as they are immutable, at 

 once enter into the category of the metaphysical 

 species of the School. If, on the contrary, science 

 can demonstrate that species are variable, then 

 the fancied identity of physiological and meta- 

 physical species immediately disappears. The de- 

 termination, however, whether living types, plant 

 or animal, are variable or permanent ; whether 

 physiological species shall be classed in the same 

 category as immutable metaphysical species, is, I 



1 In his " Summa," St. Thomas thus defines logical species : 

 " Considerandum est quod illud secundum quod sortitur aliquid 

 speciem oportet esse fixum et stans et quasi indivisibile. . . . 

 Et ideo omnis forma qu<e substantialiter participatur in subjecto, 

 caret intensione et remissione." " Summa," pars I, qusest. 52, 

 art. i. 



