136 ON STRUCTURE 



The wing neuration is always rather trouble- 

 some, as various authors use different names for 

 the veins and cells. To begin with the anterior 

 wing (e), there are four nerves which start from the 

 base and run horizontally ; the first of these, 

 which forms the anterior margin of the wing, is 

 called the costal nervure (1) ; immediately below 

 this, and running almost parallel to it with scarcely 

 any space between them, is the post-costal ner- 

 vure (2) ; these end in the stigma (s), a dark in- 

 crassation towards the apex of the wing ; from 

 the stigma a nerve, curving first downwards and 

 then up to the anterior margin of the wing, encloses 

 the marginal cell (A). Below the post-costal ner- 

 vure, and situated about the centre of the wing, 

 is the third longitudinal nervure called the median 

 nervure (3) ; behind this again runs the posterior 

 nervure (4), and behind that the actual margin of 

 the wing which is not provided with a protecting 

 nervure, but is only folded back so as to receive 

 the hooks of the posterior wing. Across the wing 

 at, roughly, about a third of its length from the 

 body runs the basal nervure (5) ; this extends in 

 a somewhat zigzag line from the post-costal to 

 the posterior nervure crossing the median, and 



