THE EXTmCT MAMMALIA. 295 



plants, the species of organic beings, as well as the various natu- 

 ral divisions into which these organic beings fall, have not always 

 been as we see them to-day, but they have been produced by a 

 process of change which has progressed from age to age through 

 the influence of natural laws ; that, therefore, the species which 

 now exist are the descendants of other species which have existed 

 heretofore, by the ordinary processes of reproduction ; and that 

 all the various structures of organic beings, which make them 

 what they are, and which compel them to act as they now act, 

 are the result of gradual or sudden modifications and changes 

 during the periods of geologic time. That is the first phase or 

 aspect which meets the naturalist or biologist. 



Another phase of the question relates to the origin of that life 

 itself which is supposed to inhabit or possess organic beings. 

 There is an hypothesis of evolution which derives this life from 

 no-life, which derives vitality from non- vitality. This is another 

 branch of the subject, tt) which I can not devote much attention 

 to-day. 



There is still another department of the subject, which relates 

 to the origin of mind, and which derives the mental organization 

 of the higher animals, especially of man, from pre-existent tj^es 

 of mental organization. This gives us a genealogy of mind, a his- 

 tory of the production or creation of mind, as it is now presented 

 in its more complex aspects as a function of the human brain. 

 This aspect of the subject is, of course, interesting ; and upon 

 it I can touch with more confidence than upon the question of 

 the origin of life. 



Coming now to the question of the origin of structures, we 

 have by this time accumulated a vast number of facts which have 

 been collated by laborious and faithful workers, in many countries 

 and during many years ; so that we can speak with a good deal of 

 confidence on this subject also. As to the phenomena which 

 meet the student of zoology and botany at every turn, I would 

 merely repeat what every one knows — and I beg pardon of my bio- 

 logical friends for telling them a few well-known truths, for there 

 may be- those present who are not in the biological section — the 

 phenomena which meet the student of biology come under two 

 leading classes. The first is the remarkable fidelity of species in 

 reproducing their like. ''Like produces like," is the old theo- 

 rem, and is true in a great many cases ; just as coins are struck 

 from the die, just as castings are turned out from a common 



