1 8 GERMINAL SELECTION. 



so on. It is an undoubted fact that such relations 

 exist, that the markings frequently exhibit a certain 

 symmetry, that — to use the words of the most recent 

 observer on this subject, Bateson^ — 2. meristic repre- 

 sentation of equivalent design-elements occurs. But 

 I believe we should be very cautious in deducing laws 

 from these facts, because all the rules traceable in the 

 markings apply only to small groups of forms and are 

 never comprehensive nor decisive for the entire class 

 or even for the single sub-class of diurnal butterflies, 

 in fact, often not so for a whole genus. All this 

 points to special causes operative only within this 

 group. 



If internal laws controlled the marking on butter- 

 flies' wings, we should expect that some general rule 

 could be established, requiring that the upper and 

 under surfaces of the wings should be alike, or that 

 they should be different, or that the fore wings should 

 be colored the same as or differently from the hind 

 wings, etc. But in reality all possible kinds of com- 

 binations occur simultaneously, and no rule holds 

 throughout. Or, it might be supposed that bright 

 colors should occur only on the upper surface or only 

 on the under surface, or on the fore wings or only 

 on the hind wings. But the fact is, they occur indis- 

 criminately, now here, now there, and no one method 

 of appearance is uniform throughout all the species. 

 But the fitness of the various distributions of colors is 

 apparent, and the moment we apply the principle of 

 utility we know why in the diurnal butterflies the 

 upper surface alone is usually variegated and the under 

 surface protectively colored, or why in the nocturnal 



^Materials for the Study of Variation with Especial Re- 

 gard to Discontinuity in the Origin of Species. London, 1895. 



