DEVELOPMENT OF THE ACCESSORY TUBULES OF INSECT SPERM FLAGELLA

The sperm flagellum in most insects has nine accessory tubules, which are formed onto the simple 9 + 2 axoneme during late spermiogenesis. W e have earlier shown that there is a considerable diversity in the app earance of these tubules, among others with regard to the number of pr otofilaments seen in their wall. The accessory tubules of the examined strepsipteran species seem unique in having a wall that is an incompl ete cylinder of protofilaments. In order to investigate whether access ory tubules of different kinds are formed by the same or different rou tes, we have studied the growing axoneme in spermatids from insect gro ups with various types of accessory tubules. In all cases the accessor y tubules were seen to be formed as extensions on the B-subtubule near the fourth protofilament counting from its outer border. Although phy logenetic considerations indicate that accessory tubules have been acq uired and lost at several occasions in class Insecta, the morphogeneti c events during accessory tubule formation seem to be fundamentally th e same in all instances.