STRUCTURE. 
555 
five cells can be seen, which are the five posterior cells, the front one being 
called the first. 
On comparing the figure of the mosquito’s wing (fig 352), we see 
that the media is only two-branched, and there is no posterior cross¬ 
vein, and thus no closed discal cell. Also the cubitus 2 and anal veins 
do not coalesce, but remain quite separate, leaving the anal cell open 
at the margin of the wing. 
The house-fly type of wing (fig. 423 & PL LXVIII) has diverged a 
good deal from that exhibited by the horse-fly and mosquito. This is 
thought to be due to the coalescence, or growing together inwards from 
the margin, of certain veins at some period in the past history of house¬ 
flies, and a consequent reduction in the number of veins apparently 
present. 
There is only one submarginal cell (i.e., the radius is 3—instead of 
4-branched). The media is 2-branched, the first branch turning up so as 
nearly to close the first posterior cell. The branching of the media occurs 
quite near the base of the wing, and the posterior cross-vein is rather near 
the margin, so that the discal cell is large. The posterior branch of the 
media has coalesced along nearly its whole length with the anterior 
branch of the cubitus, while the short posterior branch of the latter joins 
the anal vein near the base of the wing, the anal cell being thus quite 
short (i.e., “closed remote from the margin”). Just behind the anal 
vein is a small second anal vein. There is another system of naming the 
veins which is very often used, and which is more convenient when 
dealing with the specialized wings of most Cyclorhapha ; we therefore 
give it for comparison and reference. The names of the cells and cross¬ 
veins are the same : the others as follows :— 
Costa 
.. 
.. Costa. 
Subcosta 
.. Auxiliary. 
Radius 
1 
.. 1st Longitudinal. 
33 
2 
.. 2nd Longitudinal. 
33 
3 
.. 3rd Longitudinal anterior branch. 
33 
4 
.. 3rd Longitudinal posterior branch. 
Media 
1 
.. 4th Longitudinal anterior branch. 
2 
.. 4th Longitudinal posterior branch. 
3 
.. 5th Longitudinal anterior branch. 
Cubitus 
1 
.. 5th Longitudinal posterior branch. 
