ABSTRACT
Dissociation and recombination experiments in vitro were found useful for analysing inductive tissue interactions involved in lens differentiation in the chick.
When the presumptive cephalic region (epiblast plus hypoblast) of the embryo at pre-definitive streak to one-somite stage is cultivated in vitro combined with the dermis isolated either from the dorsal skin of 6·5-day embryo or from the 13·5-day tarsometatarsal skin, a lens with fibres or lentoid is produced in the epiblast. In no case is there an optic vesicle present in the explant.
When the presumptive cephalic region (epiblast plus hypoblast) is cultivated without dermis, the lens is no longer formed.
If the epiblast alone, dissociated from the hypoblast of the presumptive cephalic region, is recombined with the dermis of the 6·5-day dorsal skin, lenses or lentoids fail to develop.
Cultivation of the epiblast alone cannot cause differentiation of the lens or lentoid.
The dermis can be replaced by other mesenchymes or embryonic organs : gizzard mesen-chyme, mesonephros, sclerotome, liver and neural retina, though they are less effective than the dermis in producing lenses or lentoids in the epiblast.
It may therefore be concluded that the lens is induced in vitro by the actions of at least two factors: the epiblast first becomes competent under the specific influence of the hypo-blast of the cephalic region. The lens will then differentiate from the competent epiblast by the non-specific action of various tissues such as the skin dermis, mesonephros, or sclerotome.
The primary stage of lens induction (action of the hypoblast on the epiblast) seems not yet completed by streak stage.
