BOMicRY. 75; 



their primitive history, we should hardly go astray if we assume that 

 the ancestors of the Protoi/onius species were forest-butterflies, and 

 already possessed an under surface resembling a leaf. By this device, 

 they were protected when at rest. Afterwards, when this protection 

 was no longer sufficient, they acquired, on their upper surface, the 

 coloration of the exempt species, with which they most harmonised 

 in abode, habits of life, and outward appearance." 



But when we have granted all this, when we have agreed that this 

 is, as Weismann avers, sufficient to " explain why these butterflies did 

 not acquire the coloration of the Heliconids on the under surface;" 

 when we have further agreed with him that " the reason is, that in 

 the attitude of repose, they are already protected, and that in an 

 admirable manner," we appear to have got no further as to how the 

 duplex coloration originates, and we would suggest that our previous 

 explanation, viz., the independence of the scale-determinants of the 

 wing, is quite sufficient to explain how the differences originally came 

 about, natural selection having determined the respective directions 

 which the two surfaces should take. 



Weismann probably would answer that he does not question this 

 view, that he is only asserting that utility explains " why," and not 

 " how." He repeatedly asserts, however, that selection and utility 

 originate the colour-patterns, which is true in a general (and only in a 

 general) sense, so far as actual patterns do not exist as such until 

 natural selection forms them out of the crude material at its disposal. 

 Nor do we agree with those who, Weismann says, assert that "the 

 colour patterns of the butterfly's wings have originated from internal 

 causes independently of selection," for we believe that there are at 

 least two processes of selection engaged before the ultimate production 

 of any colour pattern : — (1). Selection (internal) among the biophors 

 themselves, before the crude material is ready prepared, as it were, for 

 the action of (2) natural selection (external), to mould it into some 

 particular pattern. 



The explanation offered by Weismann as to why exempt (nauseous) 

 diurnal butterflies should be coloured alike on the upper and under 

 surfaces, and should never resemble, in the attitude of repose, their 

 ordinary surroundings, appears sound. It is that "it is a much 

 greater protection to be despised when discovered, than to be well, or 

 very well, but never absolutely, protected from discovery." 



Weismann holds that the implications of the apparently trivial 

 and commonplace statement that " butterflies are protectively coloured 

 on the under surface, militate against the inner motive and formative 

 forces which are ever and anon appealed to." We were inclined at 

 first to disagree with this, on the ground that internal forces were 

 responsible for the variations which natural selection has utilised in 

 order to build up the pattern which has rendered the butterfly pro-. 

 tectively coloured. This, however, hardly seems to be the point 

 raised, and we agree that the actual protective pattern has been 

 produced by external and not by internal forces. 



On this subject, Weismann goes on to say : — " No less than sixty- 

 two genera are counted to-day in the family of diurnal butterflies 

 known as the Nymphalid.e. Of these, by far the larger majority 

 are sympathetically coloured underneath, that is, they show in the- 

 posture of rest the colourings of their usual environment," He then: 



