The embryonic history of the lens in bdellostoma stouti in relation to recent experiments

Spemann,' Lewis: and others, have shown by experiments on amphibian embryos that there is no localization of lens-forming material in any given area of the ectodenn, and that the formation of a lens depends directly upon the stimulation of the ectoderm by a contact with the optic-cup.Spemann has since discussed the question of the self-differentiating power of the lens and concluded from a consideration of Schaper's ' experiments on the frog that the lens is not self-differentiating, but that a durable influence or contact of the optic-cup is necessary to cause the lens-plate or lens-bud to develop into a typical lens.Le Cron has lately shown by a series of convincing experiments that the lens in Amblystoma is not self-differentiating.He found when the optic-cup was artificially removed from below the lens-plate, lens-bud, or lensvesicle that the lens structure soon ceased to further differentiate and commenced to undergo degeneration.In most of these experiments the authors have considered the possibility that the injury caused by theaoperation might be responsible for the failure of the lens to form, although their methods and care have been s&cient to convince one that such was not the case.