The ComstockâÂÂNeedham system is a naming system for insect wing veins, devised by John Comstock and George Needham in 1898. It was an important step in showing the homology of all insect wings. This system was based on Needham's pretracheation theory that was later discredited by Frederic Charles Fraser in 1938.
The Comstock and Needham system attributes different names to the veins on an insect's wing. From the anterior (leading) edge of the wing towards the posterior (rear), the major longitudinal veins are named:
Apart from the costal and the anal veins, each vein can be branched, in which case the branches are numbered from anterior to posterior. For example, the two branches of the subcostal vein will be called Sc<sub>1</sub> and Sc<sub>2</sub>.
The radius typically branches once near the base, producing anteriorly the R<sub>1</sub> and posteriorly the radial sector Rs. The radial sector may fork twice.
The media may also fork twice, therefore having four branches reaching the wing margin.
According to the ComstockâÂÂNeedham system, the cubitus forks once, producing the cubital veins Cu<sub>1</sub> and Cu<sub>2</sub>. According to some other authorities, Cu<sub>1</sub> may fork again, producing the Cu<sub>1a</sub> and Cu<sub>1b</sub>.
As there are several anal veins, they are called A1, A2, and so on. They are usually unforked.
Crossveins link the longitudinal veins, and are named accordingly (for example, the medio-cubital crossvein is termed m-cu). Some crossveins have their own name, like the humeral crossvein h and the sectoral crossvein s.
The cells are named after the vein on the anterior side; for instance, the cell between Sc<sub>2</sub> and R<sub>1</sub> is called Sc<sub>2</sub>.
In the case where two cells are separated by a crossvein but have the same anterior longitudinal vein, they should have the same name. To avoid this, they are attributed a number. For example, the R<sub>1</sub> cell is divided in two by the radial cross vein: the basal cell is termed "first R<sub>1</sub>", and the distal cell "second R<sub>1</sub>".
If a cell is bordered anteriorly by a forking vein, such as R<sub>2</sub> and R<sub>3</sub>, the cell is named after the posterior vein, in this case R<sub>3</sub>.