Abstract
Harrison 1 demonstrated in Amblystoma punctatum that lens development was suppressed if the eye rudiment was excised just before or immediately after the closure of the neural folds, but that the same presumptive lens ectoderm would form lens tissue if grafted to other parts of the head. This indicated that the lens was established very early even though a prolonged association with the eye insured better development. He also showed that at this time body and head ectoderm was not transformed into lens if grafted over these eye centers. In stages after the closure of the neural folds this was corroborated by Beekwith 2 and Stone and Dinnean. 3
The present report involving 60 experiments demonstrates lens induction by the eye in this salamander and shows how the various lens-eye relationships in cyclopia can be explained on this basis.
The presumptive lens forming region in the open neural plate (Harrison stages 15 and 16) was completely excised on the right side and replaced by ectoderm which was taken from the ventral pole of Harrison stage 12 to 13, previously stained in Nile-blue sulphate. The blue ectoderm later covered the entire side of the head including the eye. The latter induced a lens in the grafted ectoderm. In his-tological sections the lens contained the blue dye, therefore leaving no doubt as to its origin.
In one group of experiments in this series the prechordal substrate under the neural plate (Harrison stage 15) was excised in the manner described by Mangold 4 and Adelmann, 5 while in another group, eggs (Harrison stages 8 and 9—when involution of blastopore begins) were placed in lithium chloride (0.4% solution) for 24 hours.
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