This monograph clarifies many of the ambiguities concerning cephalochordate development in general, and that of Branchiostoma lanceolatum, the lancelet, in particular. Most of these came about because the majority of studies were performed in a time when the electron microscope was not yet widespread, and researchers resorted to light microscopy instead. Many features of the early embryonic stages of cephalochordates are below the resolving power of light microscopes.
This study therefore provides a detailed morphological description based on electron microscopy of complete serial sections of developmental stages of cephalochordates.