ABSTRACT
Distribution of pigment-forming cells has been analysed in sixteen individuals (six embryos, nine newborn young, one adult animal) developed from fused eggs differing in genotype for pigmentation (pink eye dilution versus agouti).
The following structures were examined: the outer layer of the retina (all individuals), choroid and Harderian gland and skin from various regions of the body (postnatal individuals).
In the six embryos, pigment was revealed in their retinae but since the development of pigmentation was still in progress at that age the genotype of non-pigmented cells could not be identified.
In seven out of the nine newborn young the outer layer of the retina was a mosaic with pigmented and non-pigmented cells intermingled. In the two other animals the outer layer of the retina was homogenous, being of’pink’ type in one animal and of ‘agouti’ type in the other.
In the adult animal the outer layer of the retina of one eye seems to be composed of two types of cells. The difference of pigmentation between them is quantitative only, the colour and shape of the granules being the same and typical for the agouti (hybrid) component. To postulate the chimaeric constitution it would be necessary to assume, therefore, that the cells derived from the LAB Grey component (pink-eyed) have been in some way induced by the neighbouring hybrid cells to synthesize pigment typical of the latter.
In all newborn animals, except the one with non-pigmented eyes, melanocytes from the agouti component were detected in the choiroid, Harderian gland and the samples of skin examined. However, the presence of melanocytes of the other genotype could be neither proved nor rejected.
On the basis of the composition of the retinae and the distribution of pigmented melanocytes in the skin it is inferred that the majority of animals developed from fused eggs are real chimaeras, at least as far as the neural derivatives are concerned. Since pigmentation does not reveal the genetic constitution of structures of different developmental history and derivation, the chimaeric character of animals with homogenous retinae cannot be excluded.
