. The elements of experimental embryology. Embryology, Experimental; Embryology. THE MOSAIC STAGE OF DIFFERENTIATION 197 found that, although they have the capacity for regeneration, the regenerate still shows the defective organisation ( with regard to the ventral fin membrane). It appears in these cases that the organism cannot regenerate a structure which has never been formed in its own ontogeny: a fact of great interest in itself and. .>â 'â - \^ ' ',' .^- ^^. Fig. 94 Effect of extirpation of tail-rudiment at early stage, in Triton; left, the operation; right, the resulting larva,
. The elements of experimental embryology. Embryology, Experimental; Embryology. THE MOSAIC STAGE OF DIFFERENTIATION 197 found that, although they have the capacity for regeneration, the regenerate still shows the defective organisation ( with regard to the ventral fin membrane). It appears in these cases that the organism cannot regenerate a structure which has never been formed in its own ontogeny: a fact of great interest in itself and. .>â 'â - \^ ' ',' .^- ^^. Fig. 94 Effect of extirpation of tail-rudiment at early stage, in Triton; left, the operation; right, the resulting larva, with total absence of tail. (From Schaxel, Arch. Entwmech. l, 1922.) with an important bearing on the problem of gradient-fields, to be discussed in Chap. x. It is still, however, uncertain whether this limitation is universal.^ 1 Cases are known in which an abnormal limb (which owes its abnormality to the fact that its rudiment was grafted at an early embryonic stage and failed to develop normally) can after amputation regenerate a normal limb (Swett, 1924). Clearly, the conditions here are different from those in which a structure is ab- normal, imperfect, or absent as a result of retnoval of its rudiment. The abnor- mality of the grafted limb is a consequence of some local conditions due to the experiment, and does not reflect any intrinsic restrictions of potency in the limb- rudiment. Consequently, when a new set of conditions supervenes as a result of amputation, these potencies are present and able to control the regeneration of a normal Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Huxley, Julian, 1887-1975; De Beer, Gavin, Sir, 1899-1972. New York [Hafner Pub. Co. ]
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