Les organes perisympathiques des dipteres

Abstract

This paper describes the perisympathetic organs (PO) of 8 families of Diptera, inc. Culicidae, Tabanidae and Muscidae which, between them, represent the principal subdivisions of the order. In general, the PO of these insects do not form large obvious structures and so they are not easily localized. Histologically, however their structure is classically that of neurohaemal organs. The thoracic PO differ from those found in the abdomen. In the thorax, PO associated with the fused ganglia are of the evolved type, while in the abdomen where the nervous system is not concentrated, the PO are of the primitive type. In Glossina, where the abdominal ganglia fuse with those of the thorax to form a single thoraco-abdominal ganglionic centre, there is a peculiar median abdominal PO. It consists of neurosecretory endings located between the glial cells of the perineurium, in the postero-dorsal part of the ganglionic centre. It seems that it comes from metameric internal organs which have lost their connective tissue boundaries. This unusual arrangement probably reflects the extreme degree to which the nervous system is concentrated in this insect. In several of the species studied, peripheral neurones were found lying close to the neurohaemal areas. Their function is discussed.