The retrocerebral endocrine complex in Diptera

The retrocerebral endocrine glands were studied in 20 insects belonging to the three suborders of Diptera. The CC-CA complex either takes the form of a ring gland, or consists of paired CC and CA. In the suborders Nematocera and Brachycera, both types of organization are to be seen, but only ring gland organization is present in members of the suborder Cyclorrhapha. NCC I and NCC II are found only in insects with paired CC and CA. The histology of the CC and CA is described. NCA1 is clearly discernible in species with paired organization. NCA2 was seen in only one species (Tabanus speciosus), but no swelling was observed on this nerve. NAA and NAO were not present in any of the 20 species studied.