692 Mr. R. C. L. Perkins on the 



the bands more faint or altogether absent in the female. 

 In the Crabronidae the females seem harder to shift 

 from the normal, and I believe that this kind of ' con- 

 servatism ' is really true of the female sex among insects 

 in general. For instance, in N. rubrocaudahis, the male 

 has characteristically dark wings with blue iridescence, 

 but the female has clear wings. In many of the species, 

 the male wings are darker than the female, as though it 

 were hard for the latter to become changed, and this is the 

 same with the thoracic spots, which in three species of 

 Nesocrahro with black abdomen are altogether wanting or 

 reduced in size in the male, while they are in two species 

 always, or nearly always, present in the female, and in the 

 third are present in some varieties. They seem to give 

 up these characters with great difficulty. 



I should think it much more probable on the Mullerian 

 theory that ' the predominance of female mimicry in 

 butterflies ' is due to the necessity of a long life (for egg- 

 laying) for the females, and not to 'a greater female 

 variability in features associated secondarily with sex.' 



On the Mullerian theory, I should say that the presence 

 of numerous reversional examples in the Hawaiian species 

 is likely to be due to the fact that nowadays the bird 

 competition has become ineffective. These reversion 

 colours, in Odynerus at least, are more often found in 

 males than females ; I should say because the females, 

 having once arrived at a stable condition, are less easily 

 changed, i. e. more ' conservative.' There is a war between 

 the greater need to change in the female and the ' con- 

 servatism,' doubtless, in producing Colour-groups, just as 

 sexual selection may cause interference. There is not the 

 least doubt that in Hymenoptera generally, the males are 

 of very transitory appearance compared with the females, 

 the difference in length of life often being one of months. 



Facts and Arguments for and against Mullerian 

 Mimicry as the Interpretation of the Colour- 

 groups of Hawaiian Aculeates. 



[From this point the passages from Dr. Perkins' letters 

 are grouped under heads.] 



Nov. 8, 1911. 



I have myself for years considered the Batesian theory 



