Abstract
The embryo of Amblystoma punctatum has been reported as one of those in which the ectoderm normally giving rise to the lens is dependent upon the continued influence of the optic vesicle to effect its differentiation. 1 It was surprising, therefore, to find that in certain experiments, directed toward the study of the gills, lenses developed from the proper ectoderm when transplanted to regions far from the eye.
There are obviously two ways of testing the independence of lens differentiation: one is to take away the eye rudiment as has been done in previous experiments (Spemann, Lewis, Le Cron); the other is to transplant the lens-forming ectoderm to another region of the embryo. The present experiments upon Amblystoma show that the results may be different in the two cases.
Excision of the eye rudiment in the medullary plate stage is followed by suppression of the lens. Likewise, if the optic vesicle is removed immediately or shortly after closure of the medullary folds, the lens fails to develop, as shown by Le Cron.
If, however, this same lens ectoderm is transplanted to other regions of the head, a well differentiated lens will develop, provided the ectoderm is taken from the eye region after closure of the medullary folds. Contact between optic vesicle and ectoderm has at this time been established, though the two are not adherent and may be readily separated without cells from one layer sticking to the other. If the lens ectoderm is taken in earlier stages, small and not fully differentiated lenses are sometimes but not always formed.
Barring one or two questionable cases, there is no evidence that, in Awzblystoma, ectoderrn from other parts of the head or from the trunk can give rise to a normal lens.
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