IV WALLACE'S OBSERVATIONS 141 



Specially striking are the peculiarities mentioned by 

 Wallace in the form of the anterior wings in the species of 

 Papilio of Celebes ; the anterior wings are in general more 

 elongated and sickle-shaped, the front margin is more strongly 

 curved than in the species of other districts, and usually makes 

 a sudden bend, an angle, near the base of the wing. 



As this peculiar form of the wing in Celebes occurs not 

 only in species of Papilio but also in Pieridse and species of 

 other families, Wallace believes its origin is due to an advan- 

 tage in the struggle for existence ; he supposes that these 

 large butterflies must, in consequence of the sickle-like shape 

 of the anterior wing and its curved front edge, be able to turn 

 suddenly in flight with greater ease, and in this way baffle 

 their pursuers. He thinks this the more probable because 

 the only Papilio in Celebes which does not possess this 

 peculiarity in the wings, P. Polyphontes of the Polydorus 

 group, appears to be protected in other ways. 



This is certainly possible, although considerations already 

 noticed, showing that large wings actually protect butterflies 

 from capture during flight, are opposed to it, and although 

 Wallace is unable to name the pursuers which are baffled. 

 For the very reason that the same peculiarity occurs in differ- 

 ent but allied families, it should rather, however, be regarded 

 as the consequence of a direction of evolution, a phyletic 

 growth determined by peculiar conditions of climate or 

 nutrition, and similarly with the disappearance of tails 

 towards the East. The differences in size also of butterflies 

 on islands probably have their causes in differences in the 

 abundance of nutritive resources. 



With regard to the tails, to Wallace's observations I am 

 able to add that it is the higher species of the genus Papilio 

 in which they disappear, so that we have to deal with their 

 disappearance from the genus. 



Moreover, the peculiarities of the colouring of butterflies 



