Haecl<el'sEmbryos & Evolution

fully developed,widely dissimilar."He inferredthat all vertebrates"arethemodifieddescendantsof some ancientprogenitor,"andthat"theembryonicor larval stageshowus,moreor lesscompletely,thecondition of the progenitorof the whole group in its adult state"(Darwin 1859,pp. 338,345).Darwin'scontem-porary Ernst Haeckel called this the "Biogenetic Law, " accordingto which "ontogenyrecapitulates phylogeny. " To illustrate the law, Haeckel (1891) produceddrawingsofvertebratembryoswhichhave been widely used in biology textbooksever since (Figure1). But Haeckel'sBiogeneticLaw was discreditedby embryologistsin Darwin's lifetime (Bowler 1989); recentwork hasshownthatHaeckel'sdrawingsmis-representheembryostheypurporttoshow(Richard-son et al. 1997);and Haeckelentirely omittedthe earlieststagesof developmentin which the various classesof vertebratesaremorphologicallyverydiffer-ent (Elinson1987).Biologyteachershouldbe aware that Haeckel'sdrawingsdo not fit the facts