206 
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 stability ” 
( 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. 
