66 THE GENERAL FEATURES OF WINGS 



that are thus recognized and the abbreviations of these names that are used 

 are the following : 



Names of branches Abbreviations 



Subcosta-one Sci 



Subcosta-two Sc2 



Radius-one Ri 



Radius-two R2 



Radius-three R3 



Radius-four R4 



Radius-five R5 



Media-one Mi 



Media-two M2 



Media-three M3 



Media-four M4 



Cubitus-one Cui 



Cubitus-two Cu2 



In the case of radius and of media, each of which has more than two 

 branches, each division of the vein that bears two or more branches has 

 received a special name. Thus after the separation of radius-one from the 

 main stem of radius there remains a division which is typically four- 

 branched ; this division is termed the radial sector or Rg ; the first division 

 of the radial sector, which later separates into radius-two and radius-three, 

 is designated as radius- two-plus-three or R2+3; and the second division is 

 termed radius-four-plus-five or R4+5- Media is t^^pically separated into 

 two divisions, each of which is two-branched; the first division is media- 

 one-plus-two or Ml +2, the second, media-three-plus-four or M3+4- 



The veins of the anal area. — The three veins of the anal area, which are 

 designated as the first anal (ist A), second anal {2d A), and third anal {3d A) 

 respectively, exhibit a wide range of variation both as to their persistence 

 and as to their form when present. In wings with a reduced anal area any 

 or all of the anal veins may be lacking; on the other hand, in wings with 

 an expanded anal area some or all of the anal veins may be branched. 



In those cases where the anal veins are branched there is no indication 

 that the branching has been derived from a uniform primitive type of 

 branching, as is the case with the other branched principal veins. The 

 principal branches of either radius, media, or cubitus can be homologized, 

 when present, throughout the insect series; and, therefore, have been given 

 distinctive names; but there is no reason to believe that this can be done 

 with the branches of the anal veins. For this reason in describing a branched 

 anal vein merely the number of branches is indicated. 



In many cases where there is a reduction in the number of anal veins a 

 study of the development of the wing will reveal the manner in which the 



