58 LECTURES 



and of reason, between the lower forms of animal life on 

 the one hand and man on the other. For, I believe, as 

 great and as evident as the gap is which separates the 

 manifestations of the mental faculties of the very lowest 

 types of humanity and the very highest types of those 

 vertebrates next in order to them is simply a difference of 

 degree and not of kind. 



We have also seen, in a former lecture, how the study 

 of another primary branch of biology, or the question of 

 distribution, explains the laws which govern the dis- 

 persal of animals and plants over the face of the globe 

 and in the great bodies of water of the earth, not only 

 for existing faunae, but for the vast faunas that have 

 existed since life first appeared in the world, and which 

 are now for the most part extinct. 



Finally, in the fourth division of the science of biology, 

 or that is in aetiology, we saw how from the consideration 

 of the facts of the science we passed to the task of deter- 

 mining the causes of those facts. It is now thoroughly 

 appreciated that biological phenomena can be explained, 

 in so far as our present knowledge will permit, by consid- 

 ering the causes as simply special cases of general physi- 

 cal laws. There is no question dealt with under the 

 head of aetiology of greater importance than the investi- 

 gation of the origin of living matter, and upon entering 

 that field we meet with one group of investigators who 

 still adhere to the theory of abiogenesis, or what in real- 

 ity is the old theory of spontaneous generation, and an- 

 other group who are the -supporters of the biogenetic 

 view, which contends that all living beings have been 

 derived from pre-existing forms of life. This latter is 

 termed the theory of biogenesis. Very close reasoning is 

 done upon both sides, but at the bottom of it all it can- 

 not be said that we are in possession of any positive 

 knowledge upon the subject. Still, I believe it lies 

 within the pale of attainable knowledge, and is a problem 

 that will be satisfactorily solved by the biologists of the 

 future. 



With this brief recapitulation of the scope of biology be- 

 fore us, we now may ask of what value, as a study, does this 

 greatscience, this comprehensive department of human 

 knowledge offer to mankind at large? To properly answer 

 this it will be necessary to say a few words upon the ques- 

 tion as to wherein lies the value of the pursuit of any 

 study, and apply our finding to the pursuit of the study 

 of biology. With respect to any of the sciences, my 

 opinion has always been that the discoveries of truths 



