228
SILVIO RANZI
σ
CO
Vegetalized
Control
Animalized
FIG. 16. Changes induced by vegetalizing and animalizing substances in sea urchin
and frog (embryo shown in cross section) (from Ranzi, 1957).
FIG. 17. Urea-induced animalization in sea urchins (Sphaerechinus and Arbacia) (from
Pedrazzi, 1957).
was analysed by Runnström (1928), Lindahl (1936) and Gustafson
(1954); vegetalized embryos show a smaller ciliary tuft than the controls, and they develop into larvae in which the ectoderm is reduced
while the endoderm is hyperdeveloped and in certain instances protrudes
(exogastrulae). Animalized embryos develop a very large ciliary tuft;