The sperm tail axoneme studies at high magnification

The axoneme of the insect sperm tail is usually described with the 9+9+2 formula which refers to 9 accessory tubules surrounding the classical 9+2 organelle. When studied with traditional methods the 9+9+2 pattern is seen as a more or less uniform entity. We describe here some techniques, which show that the axoneme actually is far from uniform and has a structure that in most cases is specific for the insect order. These techniques include fixation with a glutaraldehyde-tannic acid mixture and computer-aided image analysis. Several findings are reviewed here, for instance a non-equidistant distribution of the 13 protofilaments in the wall of axonemal A-tubules, the elliptical shape of the A-tubules and of the accessory tubules of the three related insect orders Psocoptera, Anoplura and Mallophaga, and the existence of singlet microtubules with the same characteristics as A- subtubules in insect order Thysanoptera.