Abstract
In April of the present year the writer published a report of an experimental study of regeneration in the forebrain of Amblystoma. The results showed that the removal of the cerebral hemisphere together with the end-organ normally connected with it (the nasal placode), was not followed by a regeneration of nervous tissue. On the other hand, when the cerebral hemisphere was was removed, leaving the nasal placode in place as a functionally active organ, complete regeneration of the hemisphere occurred. It was concluded that the functional activity of the nasal placode provided the requisite stimulus, at first through some hormone reaction and later through the active ingrowth of the olfactory fibers, for the regeneration of the hemisphere.
This spring the same type of experiment has been performed with the ocular complex. Amblystoma larvæ were subjected to two series of operations. In the first the right eye and the underlying mesencephalon was removed. In the second the right eye was turned back with a flap of skin and the underlying brain removed, the eye being then returned to its normal position.
The results are briefly these. The removal of the eye and the brain results in the formation across the gap of the wound of a curtain of tissue in all probability derived from the ependymal lining of the neural tube. The ingrowing fibers of the optic nerve from the left eye apparently stimulate the tissue thus formed to regenerate to a considerable extent. At the same time forward growing fibers from lower centers also afford some stimulus for regeneration, as was shown in the case of the primitive pallium of the telencephalon. The tissue thus regenerated is very similar in its organization to that normally found, except that important optic areas are lacking.
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