On the Constitution of the Maxillae and Labium in Mecoptera and Diptera

The interpretation of the composition of the maxillae and labium in Diptera requires comparison with corresponding parts in Mecoptera. Confusion has arisen in the past owing to neglect to take into consideration important features afforded by the musculature.In Mecoptera the maxilla is typically complete, both galea and lacinia being present: there is no evidence that these two lobes represent a divided galea. The labium consists of a pre-and postmentum, the former bearing two-segmented labial palpi. There is no ligula.The small mecopterous family Nannochoristidae shows coenogenetic characters and in these it deviates from the usual mecopterous type and foreshadows characters of the Diptera. This contention is borne out by the maxillae and labium.Among Diptera the more primitive families of Nematocera show characters in common with the Nannochoristidae.It is concluded that the maxillary lobe of Diptera is the lacinia, the galea always being undeveloped. The labella are formed of the two-segmented labial palpi, both paraglossae and glossae being absent.