Moulting of mechanoreceptive hair sensilla of Lepisma saccharina (Zygentoma) and Machilis spec (Archaeognatha)

In all insects investigated hitherto the mechanoreceptive hair sensilla possess the same organization plan, There are differences in the moulting process of hemimetabolous insects, While the functions of the three enveloping cells are corresponding, the position of the moulting porus is different, In Gryllus and Periplaneta the moulting porus is situated at the base of the hair, in Machilis 25 mu m above the base of the hair, In Lepisma, however, the moulting porus is located at the tip of the hair shaft, Comparison of mechano- and contactchemoreceptive hair sensilla shows that the position of the moulting porus in primitive ectognathous insects represents an argument for the close morphological and phylogenetical relationship between both types of sensilla, Interpreting our results, the original position of the moulting porus is at the tip of the hair sensilla. In mechanoreceptors, where the moulting porus is located at the base of the hair, the original tip of the hair (position of the moulting porus) is overgrown at the side by a 'secondary hair process'.