1 98 THE WONDER OF LIFE 



their death, e.g. the moths to the candle, and that some 

 (e.g. galvanotropism) are not known to be of use to their 

 possessors, but there seems much evidence that the com- 

 bination of tropisms normally exhibited by any particular 

 living creature is well adapted to the ordinary conditions 

 of its life. The particular combination is reasonably 

 referred to the work of selection. 



Beyond Tropism. — The question which one would 

 like to be able to answer is, how far the conception of 

 tropisms and the like suffices to cover what is observed of 

 the ways of the lower animals. Is tropism all, or is there 

 a gradual emergence of something more, which requires 

 other formulae ? Is there the beginning of genuine 

 behaviour ? When a monkey's bonne-bouche is hidden 

 in a vessel of a particular shape and colour, which is then 

 placed among other vessels of other shapes and colom, 

 the creature proceeds to look for it at random. But as the 

 experiment is repeated and repeated, with due precautions, 

 the monkey's tentative searches become fewer, till finally 

 it goes straight for the proper vessel. In this method of 

 trial and error the monkey doubtless uses its brains ; is it 

 possible that the same sort of method may be exhibited 

 by animals which are very far from having any brains at 

 all? 



The experiments of Jennings are in favour of an affirma- 

 tive answer. They go to show that some Infusorians 

 practise in a simple way this method of trial and error, 

 and thus make a step beyond tropisms. The Infusorian 

 Oxytricha fallax was observed advancing towards a warm 

 region of the water ; it recoiled, turned slightly on itself, 

 and advanced again. It met the warmth again and 

 repeated the same reaction, altering the direction a httle. 



