Reasons for Belief. 231 



etc., p. 109) first suggested the most plausible reason, 

 viz. : that the indiscriminate use of wings might 

 prove injurious to an insular species by tempting it 

 out to sea and to destruction, so that the loss of the 

 power of flight is a positive advantage to the species. 

 The argument against this explanation, viz.: that 

 insular species should be gifted with strong powers 

 of flight to fortify themselves against being blown to 

 sea in heavy gales, has little force, because either 

 requirement may be fulfilled ; and, in reality, where 

 flight is absolutely necessary, as in the majority of 

 Lepidoptera, and flower-frequenting Coleoptera, the 

 wing capacity, in insular species, is actually increased, 

 or correlated with a diminution of bulk ; whereas, in 

 those less dependent on aerial progression, natural 

 selection would decrease wing-power, and there 

 would be just such a correlated increase of bulk as is 

 generally the case. 



The principle he laid down, that the accidental 

 introduction of organic beings amongst others to 

 whose interest they are hostile, may be a powerful 

 means of keeping the latter in check, and of finally 

 destroying them, finds vivid exemplification in in- 

 sects, as I have shown in discussing those imported 

 into this country.* 



He gave reasons for the belief (now generally 

 accepted) that the usual gaudy colouring of inter- 

 tropical insects is not related either to the heat or 

 light of those zones, but rather to the conditions of 

 existence being generally favourable to life. (" Jour- 



* " Second Annual Report on the Insects of Missouri,". 1879, pp. 

 8-13. 



