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. 



