9 
else to do this most difficult work ; to adopt any other than his 
classification now would cause endless confusion. 
In critically examining the venation, e.g., the position and 
relative size of the cross-veins, the wing should be mounted in a 
drop of olive or castor oil, on a slide with a cover glass ; all the 
cross-veins are then seen to advantage ; with an eve piece 
micrometer their size can be determined. 
