32 THE entomologist's record. 



represent the same spots or streaks, so that we can predict from the 

 appearance of a point at one spot, the appearance of another similar 

 point at another, and so on. It is an undoubted fact that the mark- 

 ings frequently exhibit a certain symmetry," or, as Bateson" puts it, 

 " a meristic representation of equivalent design elements occurs." 

 Yet, Weismann thinks that " we should be 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 for a whole genus. All this points to 

 special causes operative only within the group." 



We are not inclined to lay so much stress as Weismann, on the 

 facts ho points out. He has himself previously stated that the 

 inherited patterns have been greatly modified, that the wing was 

 " even at its origin, far from being a tahnla ram, but was a closely- 

 written and fully-covered sheet, on which there was no room for new 

 writing until a portion of the old had been efl'aced." It appears to us 

 to want only a very slight application of this principle, in various 

 directions, to understand why the rules traceable in the markings 

 apply only to small groups of forms. At the same time we are inclined 

 to agree with him, that some more general characters would be trace- 

 able through a larger number of species if the markings were entirely 

 produced, governed and moulded by internal forces. 



Weismann then asserts that " if internal laws controlled the 

 markings on butterflies' 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 coloured the same as, or differently from, 

 the hind-wings. But, in reality, all possible kinds of combinations 

 occur simultaneously, and no rule holds throughout. Or it might 

 be supposed that bright colours should occur only on the upper 

 surface, or only on the under surface, or on the fore-wing, or only on 

 the hind-wings. But the fitness of the various distributions of colours 

 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 coloiired, or 

 why, in the nocturnal butterflies the fore-wings have the appearance 

 of bark, of old wood, or of a leaf, whilst the hind-wings, which are 

 covered when resting, alone are brilliantly coloured. On this theory 

 we also understand the exceptions to these rules. We comprehend 

 why Danaids, Heliconids, Euploeids and Acraeids, in fact, all diurnal 

 butterflies offensive to the taste and smell, are most brightly marked, 

 and equally so on both surfaces ; whilst all species not thus exempt 

 from persecution have the protective colouring on the under surface, 

 and are frequently quite differently coloured there from what they 

 are on the other." 



This paragraph wants examining carefully. One is struck by the 

 excellent way in which Weismann presents his facts as to the utility 

 to the individuals of the actual existing patterns of coloration which 

 are to be found in various groups of butterflies and moths. Yet, we 

 are not sure that the flrst part of the paragraph is convincing. 



* Materials for the Study of Variation with especial Regard to the DiscontinHitij 

 in the Origin of Sjjecies. London, 1895. 



