TRANSFORMISM 235 



particular instance chosen by him, but this is because 

 the case is an unfortunate one. Probably a morpho- 

 logist could find a very much better case of convergent 

 evolution — the parallelism between the teeth of some 

 Marsupials and some Rodents, for instance. If detailed 

 histological and embryological investigation should 

 show a similarity of structure and development, in 

 such compared organs Bergson's argument would re- 

 tain all its force. We should then have to assume 

 that there was a directing agency, or tendency in the 

 organism, co-ordinating, or perhaps actually producing, 

 variations. 



Mechanistic biology can suggest no means whereby 

 simultaneously occurring variations are co-ordinated : 

 let us therefore think of these variations as occurring 

 independently of each other, and let us ignore the 

 difficulty of the infrequency of occurrence of suitably 

 co-ordinated variations. Variations are exhibited by 

 the evolving organism, and the selection of co-ordi- 

 nated series is the work of the environment. But the 

 environment is merely a passive agency, and it has to 

 confer direction on the innumerable variations pre- 

 sented to it by the organism, rejecting most but 

 selecting some. Let us think of the environment, says a 

 critic of Bergson, as a blank wall against which nume- 

 rous jets of sand are being projected. The jets scatter 

 as they approach the wall : each of them represents 

 the variations displayed by some organ or organ- 

 system of an animal. Let us think of a pattern drawn 

 on the wall in some kind of adhesive substance : where 

 the wall is blank the sand would strike, but would fall 

 off again, but it would adhere to the parts covered by 

 the adhesive paint. The sand grains: strike the wall from 

 all sides, that is, their directions are un-co-ordinated. 

 The wall is passive, yet a pattern is imprinted upon it. 



