46. CHARLES DARWIN 



butterflies], probably male and female, were chasing 

 each other in an irregular course, they passed within a 

 few yards of me ; and I distinctly heard a clicking 

 noise, similar to that produced by a toothed wheel pass- 

 ing under a spring catch.' In like manner he observed 

 here the instincts of tropical ants, the habits of phos- 

 phorescent insects, and the horrid practice of that wasp- 

 like creature, the sphex, which stuffs the clay cells of 

 its larvae full of half-dead spiders and writhing cater- 

 pillars, so stung with devilish avoidance of vital parts 

 as to be left quite paralysed yet still alive, as future 

 food for the developing grubs. Cases like these helped 

 naturally to shake the young biologist's primitive faith 

 in the cheap and crude current theories of universal 

 beneficence, and to introduce that wholesome sceptical 

 reaction against received dogma which is the necessary 

 ground-work and due preparation for all great progres- 

 sive philosophical thinking. 



In July they set sail again for Monte Video, where 

 the important question of climate and vegetation began 

 to interest young Darwin's mind. Uruguay is almost 

 entirely treeless; and this curious phenomenon, in a 

 comparatively moist sub-tropical plain-land, struck him 

 as a remarkable anomaly, and set him speculating on its 

 probable cause. Australia, he remembered, was far 

 more arid, and yet its interior was everywhere covered 

 by whole forests of quaint indigenous gum-trees. Could 

 it be that there were no trees adapted to the climate ? 

 As yet, the true causes of geographical distribution had 

 not clearly dawned upon Darwin's mind ; but that a 

 young man of twenty-three should seriously busy him- 

 self about such problems of ultimate causation at all is 



