ABSTRACT
The sea-urchin egg is characterized by a very high morphogenetic plasticity. Its trend in differentiation can in fact be controlled by means of various chemical agents. The development of the entoderm is thus favoured at the expense of that of the ectoderm by adding lithium ions to the sea-water (Herbst, 1892; Lindahl, 1936). Iodosobenzoic acid (Runnström & Kriszat, 1952) and thiocyanate (Herbst, 1892; Lindahl, 1936) have an opposite effect, i.e. they favour ectodermal development. The mechanism of segregation of the egg into the primary germ-layers might be elucidated if we knew more about the biochemical mode of action of these agents. A series of biochemical studies on lithium-treated and normal eggs and larva was therefore undertaken. The studies began on the level of amino acids and peptides and continued on the levels of enzymes and intracellular inclusions.