In order to evaluate the development of the xenoplastic eye chimerae, stages of differentiation of the normal eye inBombina variegata, Hyla arborea andTriturus alpestris between the second and ninth day after neurulation have been worked out, and the results are summarized in Table 1. 2. Four types of chimeric eyes developed after transplantation of the eye-cup anlagen: type I, species-specific donor eye cup with a host lens; type II, host lens with a chimeric eye cup which was made of donor and host material, and appeared morphologically as well as histologically uniform; type III, host and donor parts of the eye cup were each surrounded by their own tapetum nigrum, but formed morphologically a chimeric eye cup of harmonious proportion with a host lens; type IV, chimeric eye of type I with, however, an additional diminished host eye. 3. The histological differentiation of the eye cup of the chimeric eye is autonomous. 4. In the absence of a lens the differentiation of the eye cup is retarded. 5. In chimeric eyes of type I the differentiation of theTriturus host lens is normal, whereas that of theBombina host lens shows a slight retardation. 6. After transplantation of the lens anlage several donor and host lenses have frequently been found, possibly due to the autonomous reactivity of the epidermis in the different species. Chimeric or donor lenses were of rare occurrence. 7. The lens size of chimeric eyes is determined by the size and inducing capacity of the eye cup, the duration of the inductive contact as well as the species-specific size of the lens vesicle. The species-specific dimension of the eye cup acts as a limiting factor to the growth of the lens. Thus, the lens index of chimeric eyes with aBombina eye cup is larger, whereas that of chimeric eyes with aTriturus eye cup appears smaller than the indices of the two control species. 8. If a lens is not induced, a Wolffian lens may develop inBombina hosts with aTriturs eye cup. In complete chimeric eyes the regeneration of a Wolffian lens is suppressed by theBombina lens. 9. Owing to the primary incompatibility eye cups transplanted fromTriturus toHyla andRana as well as lens epidermis transplanted fromTriturus toRana are expelled. As a reaction of the secondary incompatibilityBombina eye cups inTriturus hosts start to degenerate on the 11th day after transplantation. The degeneration of eye cups fromHyla andRana donors begins even earlier. If the tapetum nigrum is fully differentiated, the implant may remain longer.
