Ontogeny recapitulates phylogeny

On page 78, Coyne quotes Ernst Haeckel's biogenetic law, saying that "ontogeny recapitulates phylogeny." Coyne backs this statement up with examples of different organism's path of embryonic development, describing how, for example, human embryos undergo development in a sequence that follows the evolution of its ancestors. Trace another organism's embryonic development and describe how it reflects this organism's evolutionary history. Discuss the concept of 'adding new stuff onto old.' in embryonic development. Is it really more efficient to have, for example, human embryos go through two different kidneys before development of the 'actual' kidney happens? Why not just skip seemingly useless developmental stages?