Description:
<jats:title>ABSTRACT</jats:title>
<jats:p>In the following pages1 certain hypotheses with regard to the evolution of segmented Triploblastica (Annelida, Arthropoda, Vertebrata), and some apparently unsegmented forms (Mollusca Brachiopoda, Sagitta, Balanoglossus) are suggested and discussed.</jats:p>