XV. 



SPONTANEOUS GENERATION. 



It h is long been the custom for the newly-installed 

 President of the British Association for the Advance- 

 ment of Science to take advantage of the elevation of 

 the position in which the suffrages of his colleagues 

 had, for the time, placed him, and, casting his eyes 

 around the horizon of the scientific world, to report 

 to them what could he seen from his watch-tower ; in 

 what directions the multitudinous divisions of the 

 noble army of the improvers of natural knowledge 

 were marching; what important strongholds of the 

 great enemy of us all, ignorance, had been recently 

 captured; and, also, with due impartiality, to mark 

 where the advanced posts of science had been driven 

 in, or a long-continued siege had made no progress. 



I propose to endeavour to follow this ancient pre- 

 cedent, in a manner suited to the limitations of my 

 knowledge and of my capacity. I shall not presume 

 to attempt a panoramic survey of the world of science, 

 nor even to give a sketch of what is doing in the one 

 great province of biology, with some portions of which 

 my ordinary occupations render me familiar. But I 

 shall endeavour to put before you the history of the 

 rise and progress of a single biological doctrine ; and 

 I shall try to give some notion of the fruits, both in- 

 tellectual and practical, which we owe, directly or in- 



