After injection of oil into the oviduct of hematophagous Diptera, the ovarioles become completely
separated from each other, allowing examination of a large number of undamaged ovarioles, an important
advantage over other techniques for accurately determining the physiological age of mosquitoes. The
technique has been simplified and improved, especially by using a sodium chloride-glycerol-formaldehyde
mixture for mounting preparations, which are more convenient and permanent for examination of the
ovarioles. The difficulties of using the technique, their possible causes, and possibilities for overcoming
them are described. Similar results can be obtained with an alternative technique, the ovariolar separation
technique, using strongly diluted Carnoys solution, which leaves ovaries in a fixed condition. Both
techniques can be used for several hematophagous dipteran groups.
