Functional design in the evolution of embryos and larvae

A function of development is to put the right kind of cells in the right pl ace at the right time. Other functional analyses help define what is right. As examples, functional analyses offer explanations for the unicellular bo ttleneck in life histories that necessitates embryos, evolutionary divergen ces in embryonic cell cycles, conditions permissive of loss of larval struc tures and consequent change in embryonic development, and the decoupled dev elopment of larval bodies and juvenile rudiments. Functional analyses also reveal the specifications required of morphogenesis, hence defining develop mental phenomena to be explained.