LECTURE XXIII 



TAXONOMIC ANOMALIES 



The current theory of descent is founded 

 mainly on comparative studies, which have the 

 advantage of being broadly inclusive and the 

 convincing effect of concurrent evidence 

 brought together from widely different sources. 

 The theory of mutation on the other hand rests 

 directly upon experimental investigations, and 

 facts concerning the actual descent of one form 

 from another are as yet exceedingly rare. It is 

 always difficult to estimate the validity of con- 

 clusions drawn from isolated instances selected 

 from the whole range of contingent phenomena, 

 and this is especially true of the present case. 

 Systematic and physiologic facts seem to indi- 

 cate the existence of universal laws, and it is not 

 probable that the process of production of new 

 species would be different in the various parts 

 of the animal and vegetable kingdoms. More- 

 over the principle of unit-characters, the pre- 

 eminent significance of which has come to be 

 more fully recognized of late, is in full harmony 



658 



