2o6 COLOUR IN NATURE chap, ix 



pression of the fact that the forms of the type or the 

 variety represent positions in which the forces of 

 division are in a condition of mechanical stabiHty" 

 ( Variation, p. 71). It can hardly be doubted that 

 this explanation has an important bearing on those 

 simple forms of patterns which are directly related 

 to segmentation, but even the approximate ex- 

 planation of the complicated colour- markings of 

 Vertebrates seems as yet impossible. " Forces of 

 division " seems too vague an expression to be of 

 much aid in their case. For some other explanations 

 of markings in Vertebrates, reference should be made 

 to Mr. Wallace's Darwinism. 



