The Bionomics of Sunlit ^l/rtcau Insects. 439 



spicuous duriug the attitude of rest. There is probably 

 a certain parallelism with cryptic under-sides, such as those 

 of our VanessidiV, which have no particular meaning in 

 flight and when the insect alights, but still remains fully 

 on the alert. The resting attitude is specialized in relation 

 to the development of cryptic colours and patterns on the 

 under-side, and in this attitude cryptic insects are always in- 

 conspicuous. Apart from the evidence of adaptation in the 

 direction of conspicuousness on the under-side of the wet 

 phases of Precis — the strongest argument for the presence 

 of some distasteful quality — the mere existence of such 

 an appearance in a palatable species is inconsistent with 

 the explanation of cryptic under-sides as the product of 

 adaptation in the direction of concealment from enen)ies. 



Tlie successful attacks of a species of lizard may be 

 analogous to other well-known instances in which special 

 enemies, such as the cuckoo, are known to devour con- 

 spicuous unpalatable insects. 



Two other arguments in Mr. Marshall's paper (Ann. 

 and Mag. Nat. Hist, ser. 7, vol. ii, July 18'J8, p. 30) 

 must be met here. First, the suggestion that the brilliant 

 colours of natalensis are due to the impunity with which 

 such a development can arise in the limited struggle for 

 existence in the stations occupied by the species, and the 

 abundance in the wet season of other insect food (loc. cit., 

 pjD. 35, 36). Such a suggestion does not explain the 

 under-side coloration, and especially the evidences of 

 adaptation in it. Secondly, Mr. Marshall meets de Nice- 

 ville's and Weismann's contention, that both seasonal forms 

 "must be adaptive, otherwise the non-adaptive form would 

 be gradually supplanted by its more favoured relative," 

 by the suggestion that the dry-season phase may be a recent 

 development which is even now actually supplanting the 

 wet phase {he. cit., pp. 3G, 37). It is, however, difficult 

 to believe, looking at the Nymphalinm as a whole, and 

 especially the nearest allies of the species under discussion, 

 that the conspicuous under-side of the wet phase is an- 

 cestral, and the cryptic under-side of the dry phase recent 

 (see p. 430), so that the argument set forth above seems 

 to me untouched. Mr. Marshall has indeed shown that 

 the dry phase of F. artaxia has actually supplanted the 

 wet phase (^naclUigcdii) in forest regions, where the 

 struggle for existence is far more uniform at all seasons 

 of the year than it is in the more open woodland country 



