EVOLUTION OF THE HISTOLOGICAL AND FUNCTIONAL STRUCTURE OF ECTODERM, CHORDAMESODERM AND THEIR DERIVATIVES IN ANAMNIA

The paper considers the appearance of differences in the structure of ''primary ectoderm'', i.e. of the presumptive ectoderm and chordamesoderm material in different chordates, and offers evidence that these differences foreshadow the structural peculiarities of early embryogenesis in different groups of Anamnia. These differences are: presence or absence of the archenteron, presence or absence of the hypochordal plate, formation of a neural tube with a cavity generated by epithelial folding or by splitting a compact rudiment.