GENERAL SUMMARY. 191 



After all, it is not proved that birds are the natural 

 enemies and captors of winged diurnal Lepidoptera. 

 The dragon-fly will catch such insects on the wing, nip 

 off their wings and devour their bodies ; but such is not 

 a common sight with reference to birds. 



However, there can be no doubt that the Tettigidfe 

 often in their colourings closely assimilate with the 

 plants they affect. Some animals have special organs 

 (chromatophores) through which they are able to vary 

 their colours at will ; but insects do not appear to 

 be so endowed, and their changes of colour must be 

 sought from other causes. 



Prof. Poulton thinks that colour in insects never 

 arises from selective agency ; but that larvae are often 

 sensitive to colour-surroundings, and nymphal colour- 

 ing is often due to larval susceptibilities. 



An unconscious change of colour, dependent on light, 

 may be exemplified in the trout, which, captured in 

 some Irish deep loughs, are very dark and almost 

 spotless, whilst those taken in the neighbouring 

 tributary streams are bright and silvery. 



Mr. F. Pascoe comes to the conclusion that, as a 

 rule, insects trouble themselves very little about con- 

 cealment.* Yet the beetle drops to the ground if 

 approached, and the Cicada ceases its chirp, and finds 

 a concealment so perfect that even clever trackers 

 mostly fail to discover the insects which obviously are 

 close at hand. It may be doubted if any change of 

 colours would secure insects from the marvellously 

 acute vision of the water-wagtail or flycatcher on the 

 feed. 



The very close resemblances between the Tettigidge 

 themselves, if they could be shown to be voluntary in 

 the insects, might be called mimicry. Some instances 

 of close resemblance between species of different 

 genera have been already alluded to. As in other 

 orders of insects, this curious faculty of simulation 

 is not always equally carried out in the two sexes 



" The ' Darwinian Theory,' p. 93. 



