Two fundamental processes of the development of insect embryos are the generation and the morphological diversification of metameric units. In Drosophila, these processes are under the control of the products of the segmentation (generation) and the homeotic (morphological diversification) genes. Molecular studies of the activity of these genes has revealed spatial and temporal patterns of expression consistent with the requirements inferred from the mutant phenotypes but, in addition, these studies have revealed transient patterns which are difficult to reconcile with those phenotypes. It is possible that these patterns reflect ancestral regulatory elements which are still operational in more primitive insects. The validity of this interpretation can be tested by comparing the embryonic development of long germ band insects like Drosophila melanogaster with that of the more primitive short germ band insects like the locust Schistocerca gregaria and by obtaining and studying locust homologues of Drosophila segmentation and homeotic genes.

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