IN DEFENSIVE COLORATION 303 



contend with another argument often employed against 

 the explanation of Cryptic and Mimetic Resemblance by 

 Natural Selection. Hypertely assumes that there are 

 unnecessary details in the resemblance, that the resem- 

 blance is perfect beyond the requirements of the insect : 

 the second argument maintains that birds are so 

 supremely sharp-sighted that no resemblance, however 

 perfect, is of any avail against them. In the meantime 

 the majority of naturalists will probably reject both 

 extremes and believe that the enemies are certainly 

 sharp-sighted and successful in pursuit, but that perfection 

 in detail makes their task a harder one, and gives to the 

 individuals possessing it in a higher degree than others, 

 increased chances of escape, and of becoming the parents 

 of future generations. 



7. Hours during which the Struggle for Life is most 

 Severe. — In any attempt to understand the details of the 

 struggle, it is essential to ascertain its relative severity 

 during the various periods of the day and night. Mr. N. 

 Annandale 1 has observed that certain Siamese insects 

 were active during the hottest hours of the day, a time 

 when the birds did not hunt for food, and that conversely 

 the same insects were rarely either seen in motion or found 

 at rest during the cooler hours of daylight, when enemies 

 were busily at work. Dr. G. B. Longstaff 2 has also 

 suggested as a result of his experience in South Africa, 

 that the Cryptic colouring, attitudes, and instincts of 

 butterflies must be considered in relation to the large 

 number of hours of daylight during which they are in the 

 condition of complete rest. 



8. The Value of Brightly-coloured Surfaces Concealed 

 during Rest. — The brightly coloured hind wings of many 

 moths (Calocala, Tryphaena, &c.) and grasshoppers 

 (Oedipoda, &c.) which flash out conspicuously when the 

 insect becomes active, and disappear equally suddenly 

 when it alights, probably serve, as Lord Walsingham 3 

 has suggested, to confuse a pursuing enemy. The same 



1 Proc. Roy. Phys. Soc, Edinb., 1900, No. xxix, pp. 439-44. 



2 Trans. Ent. Soc, Lond., 1906, p. 118. 

 s Proc. Ent. Soc, Lond., 1890, pp. 1-lii. 



