146 CONCLUSION [ch. 



combinations of these colour factors. Within the 

 limits of each group is found a definite number of these 

 factors — more in one group, less in another. But some 

 factors may be common to two or more groups, in 

 which case some of the permutations of the factors 

 would be similar in the groups and would result in 

 identical or nearly identical pattern. To take a simple 

 example in illustration, let us suppose that a given 

 group, (a), contains the eight factors A — H. Since 

 any species in the group may exhibit any combination 

 of one or more of these factors it follows that a con- 

 siderable number of different forms are possible. Now 

 suppose that another group, (/3), distinguished from 

 (a) by definite structural features, also contains eight 

 factors within the group, and that these factors are 

 F — M, Fy G, and H being common to both (a) and 

 (/S). Any combination therefore in (a) lacking the 

 factors A — E will be paralleled by any combination in 

 (j8) lacking the factors / — M. For in both cases we 

 should be dealing only with the factors jP, G, and H^ 

 which are common to each group. So again a third 

 group might have some factors in common with (a) 

 and some with (j8), and so on for other groups. In 

 this way certain of the series of colour patterns found 

 in (jS) would overlap certain of those in (a), while others 

 of the groups {^) and (a) might overlap those found in 

 different groups again. The striking resemblances not 

 infrequently found between species belonging to quite 

 distinct groups would on this view depend upon the 

 hereditary factors for pattern and colour being Umited 



