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On the Abdominal Appendages of Larvae of Trichoptera, Neuroptera, and Lepidoptera, and the Origins of Jointed Limbs


The musculature of the abdominal appendages of the larvae of Sialis and Corydalus (Neuroptera) is described, and their homologies discussed. The terminal appendages of a primitive Trichopteran, Rhyacophila sp., correspond muscle by muscle with those of Corydalus. The terminal appendages of the larvae of typical members of other families of Trichoptera are compared with those of Rhyacophila; although there is great variety of form, the same muscles can be traced in all. Similarities between th e larvae of Neuroptera and Lepidoptera arenot so close; th eresemblances are in general features which are shared with other soft blood-filled appendages such as those of Tardigrada or Onychophora. Finally the general mechanical principles governing the bending of limbs are discussed. Soft turgid appendages such as the abdominal legs of caterpillars depend on a mechanism quite unlike that of the hard, jointed limbs of other arthropods, and it is difficult to see how the one can have evolved from the other. It is suggested that a parallel evolution has taken place in the terminal appendages of Trichopteran larvae, and intermediate stages are described which suggest a wayin which the change may have come about in true appendages.