Cytological and morphological studies of the action of lithium on the development of the sea urchin embryo.

The effect of lithium ions on cleavage and development of sea urchin larvae was investigated. Lithium was found to interfere with the movements of the chromosomes at mitosis, which is also very delayed in the presence of lithium. The disturbances inflicted by lithium were observed during the course of development up to the pluteus stage.The "lithium sensitive period" coincides with the period in which the mitotic activity reaches its maximum.The rate of cleavage is reduced by lithium. In the normal untreated larva there is during the early blastula stage an "animal" trend in which the formation of cells of prospective ectodermal significance preponderates. The mesomeres were found to be relatively more affected by lithium than were the macromeres. This shift in the cleavage pattern influences the numbers of cells of ectodermal and endo-mesodermal significance.Studies were also made of morphological changes following treatment with lithium.