Z-line in the insect muscles: correlated structural and functional diversities.

The Z-line of insect muscle shows different organizations in fibres with diverse performances. The Z-line fine structure and arrangement correlated with the functions of the muscle allow the different cases to be classified in three schematic groups: Unstructured Z, typical of muscles not particularly specialized either in quick movements or in developing or maintaining strong tensions; structured Z, typical of quick synchronous or asynchronous muscles; fragmented Z, typical of the supercontracting muscles. The suggested models are brieflly discussed on the basis of their functional and evolutional meanings.