Note 462 — Chapter IX · ON CONCRETIONS, SPICULES, AND SPICULAR SKELETONS

See, for instance, the figures of the segmenting egg of Synapta (after Selenka), in Korschelt and Heider’s Vergleichende Ent­wick­lungs­geschichte (Allgem. Th., 3te Lief.), p. 19, 1909. On the spiral type of segmentation as a secondary derivative, due to mechanical causes, of the “radial” type of segmentation, see E. B. Wilson, Cell-lineage of Nereis, Journ. of Morphology, VI, p. 450, 1892.