Description:
<jats:title>Abstract</jats:title><jats:p>Lobe removal experiments show that the <jats:italic>Dentalium</jats:italic> embryo's first polar lobe is necessary for larval apical tuft and posttrochal region development. The smaller second polar lobe is necessary only for posttrochal region development. When vegetal halves of eggs are isolated before fertilization and then fertilized, they form size‐regulated first polar lobes. These polar lobes are proportional to the isolated halves in size and are necessary for posttrochal region but not apical tuft development. When vegetal halves are isolated after fertilization and then refertilized, they form polar lobes with an average volume that is less than that of normal first polar lobes but greater than that of size‐regulated polar lobes. Like normal first polar lobes, these lobes are necessary for both apical tuft and posttrochal region development. Localization of apical tuft and posttrochal region determinants occurs before fertilization and cannot be altered by the process. Polar lobe size specification occurs at first fertilization but can be somewhat modified by subsequent fertilization events. Size regulation does not affect the localization of apical tuft and posttrochal region determinants but does alter the developmental role of the first polar lobe.</jats:p>