3o 



THE YOUNG NATURALIST. 



[FEBKUAKi 



pecially the case amongst the Macro-Lepidoptera, in which the males 

 are always winged, that they appear earlier than the females and are 

 on the outlook for them and consequently any tendency in an apterous 

 direction amongst the males, would become extinct with the individual 

 and not affect the species. Amongst insects generally, apterous females 

 remain near tne place where they leave the pupa ; they attract the 

 males in various ways, sometimes by scent or light, and we can see that 

 the most vigorous males which have the best power of flight will 

 secure the females, and influence the development of the species. 

 When I spoke of light I referred to the common glowworm whose 

 female is apterous, whilst the male develops increased power of vision. 

 I think it is clear from the foregoing facts, that use and dis-use must be 

 regarded as most important factors in the production and modification 

 ot organic structure. And here we may point out an instance of local 

 conditions tending to the development of wingless insects, and shewing 

 us that though a subsequent change of conditions might have made it 

 useful to the insect to possess wings, yet once lost we cannot conceive 

 them being regained, and this may explain the existence of some 

 modern apterous forms where we might have looked for winged ones. 

 The instance I refer to is familiar to our coleopterists though perhaps 

 not to other members. Madeira is subject to strong and con- 

 tinuous winds ; it is but a small island, yet representatives of 

 over 500 species of beetles occur there ; out of these the enormous 

 proportion of two fifths are wingless. This is the more striking because 

 on the mainland the majority of these species are winged. The ex- 

 planation of this remarkable instance of adaptation to surroundings is 

 that the beetles which used their wings least, ran the least risk of being 

 blown out to sea and drowned, and thus again is forcibly illustrated 

 the truth that dis-use tends in the long-run to the loss of a once func- 

 tional organ. Amongst some bugs and all lice, the latter of which 

 shew absolutely no trace of wings, leading us to infer that they are a 

 more ancient form than the bugs whose wings are represented by four 

 small plates, we see again the effect of dis-use resulting from altered 

 conditions. 



Without repeating what I have already said so often about the 

 influence of use and dis-use in the production and modification of 

 organs, it may be well to summarize the main results of the facts, and 

 first this stands out clearly ; all insects and myriapods have had a 



