THEORY OF EVOLUTION 111 



to another factor, called antler, insufficiently 

 studied as yet. 



In the third figure (c) the wings turn up at 

 the end. This is brought about by the presence 

 of the factor cialled jaunty. 



In the fourtli figure the wings are long and 

 narrow and several of the veins are unrepre- 

 sented. This character, "strap", is very varia- 

 ble and has not vet been thoroughlv studied. 

 On the thorax there is a deep black mark called 

 trefoil. Even in the wild fly there is a three 

 pronged mark on the thorax present in many 

 individuals. Trefoil is a further development 

 and modification of this mark and is due to a 

 special factor. 



In the fifth figure (e) the wings are arched. 

 The factor is called arc. The dark color of the 

 body, and especially of the wings, indicates the 

 factor for black. 



The sixth figure (f) shows the wings 

 "curved" downwards. In addition there is 

 present a minute black speck at the base of 

 each wing, due to another factor called speck. 



In the seventh figure (g) the wing is trun- 

 cate. Its end is obliquely squared instead of 



