240 SEXUAL DIMORPHISM 



Happing its wings once or twice, and then settling on some 

 projecting twig and remaining for some time motionless, 

 usually with the wings closed, and hanging downwards. It 

 is clear, therefore, that the pattern form and the mimic spend 

 much of their time settled among bushes. 



From an observation by Mr. Mansel Weale quoted by 

 Trimen and Bowker, it would appear that all three forms of 

 the female of P. cenea may arise from the same parents in one 

 locality. The former gentleman reared all three forms from 

 a number of larvte found together, and therefore it may be 

 inferred that the three forms are the dominant types in a 

 wide range of variation in the females of a single species. In 

 other words the female is trimorphic, although the three 

 imitated forms of Danais are distinct species. To speculate 

 on the causes of this state of things is perhaps not very 

 profitable without further evidence, but it may be pointed 

 out that it does not necessarily imply selection. It is possible 

 that each form of the Papilio is related to particular conditions, 

 or they may be merely the three main types which varia- 

 bility, once set up by conditions, tends to produce. In either 

 case crossing of the forms occurs through the males, a male 

 which is the offspring of one form mating with either of the 

 others, and then the progeny resembling either the mother or 

 grandmother, but not uniting the characters of both. If each 

 variety is related to special conditions, then (as in the case of 

 the primrose) probably an individual which develops a par- 

 ticular variation-type places itself under the same conditions 

 which produced the variation, and so develops it still further. 

 If this is not the case then we must conclude that the per- 

 manent distinctness of the three forms, in spite of inter- 

 crossing, is due to physiological obstacles to the combination 

 of the characters in the same individual. 



It has been tacitly assumed by those who invented and 

 those who have adopted the theory of mimicry that the 



