Evolution aiid Taxonomy 



6i 



Fig. to. — Triprocris. 



found. Thus within a single family, or perhaps superfamily, 



the more generalized members have three anal veins in at 



least one pair of wings, 



(usually the hind _. i" ' "^' "^ 



wings), while as one 



passes to more and 



more specialized forms 



only two, or one anal 



veins are found. 



I believe that this 

 selection of the nar- 

 rower winged forms is 

 the result of the sur- 

 vival of those forms 

 that are best fitted for 

 rapid flight. A good 

 illustration of the dif- 

 ference in the powers 

 of flight between an insect with a wide anal area and one 

 in which this area has been reduced, can be found within 



the limits of a single lepi- 

 dopterous superfamily, the 

 Zygaenina. Compare the 

 power of flight of Tripro- 

 cris (Fig. lo) in which there 

 are two anal veins in the 

 fore wings and three anal 

 veins in the hind wings, 

 with that of Syntomis (Fig. 

 ii) in which there is onl}^ 

 a single anal vein in both 

 fore and hind wings. 



On the other hand, in 

 other lines of development, 

 natural selection has evi- 

 dently tended to a preserva- 

 tion of the wider winged forms ; and the widening of the wings 

 has taken place largely by a specialization of the anal area by 



■Syntomis. 



