24 LECTURES 



tion of animals and plants, and the laws that control 

 their existence. Thirdly, of the question of the hered- 

 itary transmission of characters and the laws that 

 operate in producing variation in those characters, both 

 in consecutive and non-consecutive generations. 

 Psychology and sociology are also legitimate branches of 

 this subdivison. 



Finally, under aetiology we are concerned with the 

 questions of, first, the probable origin of life upon the 

 earth, and with the causes of the phenomena of the 

 same. In the second place, with the causes of the vari- 

 ations presented on the part of animals- and plants in 

 time, as well as the history and causes of the evolvement 

 of living forms and the laws pertaining thereto. The 

 phenomena of morphology, physiology, and distribution 

 are based upon known facts, whereas much that aetiology 

 has to do with, is speculative, though often amounting 

 to a degree of probability bordering upon absolute cer- 

 tainty, inasmuch as it is in complete harmony with and 

 renders full explanation of many of the known phenom- 

 ena of the three first-mentioned grand subdivisions of 

 biology. 



Thus you will see how our science has grown and de- 

 veloped, and the manner in which the subject presents 

 itself to the minds of the best interpreters of Nature 

 to-day, and how the problems concerning life itself are 

 regarded. 



Upon the next occasion of our meeting I will endeavor 

 to lay before you the evidence we possess bearing upon 

 the question of the relation of biology to geology. And 

 in doing so I shall select the vertebrata as the group 

 wherewith to point out that relationship, at the same 

 time fully assuring you that the facts we will have to 

 deal with hold true in principle for the invertebrata as 

 they likewise do for the entire vegetable kingdom. It 

 would be impossible in the short space of time represent- 

 ed by one of our lectures to deal with this subject by 

 attempting to demonstrate the bearing of the entire 

 animal and vegetable worlds, as they now exist upon the 

 face of the earth, to the science of geology, for the range 

 is far too wide; and, as I have first said, essentially the 

 same laws obtain throughout. Although I had not the 

 pleasure, last year, of attending the lecture given you by 

 Prof. Lester F. Ward, upon palaeobotany, I feel quite 

 sure he must at that time have had not a little to say 

 respecting the affinities existing among the various 

 modern florae and those fossil plants which have been 



