It's a bug's life.
Although the mechanisms of anterior-posterior axis formation are well understood in Drosophila, both embryological and molecular studies suggest significant variation in the mechanisms generating this axis within the Insecta class as a whole.
Patel
N H
NH
Howard Hughes Medical Institute, University of Chicago, 5841 South Maryland Avenue MC1028, Chicago, IL 60637, USA. npatel@midway.uchicago.edu
D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000235:genetics*; D004330:Drosophila / Q000145:classification / Q000235:genetics; D004625:Embryo, Nonmammalian; D005260:Female; D018392:Genomic Imprinting; D007313:Insecta / Q000145:classification* / Q000196:embryology / Q000235:genetics*; D008297:Male; D010802:Phylogeny