Anomalies in Regeneration of Paramecium*

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Abstract
Using two different stocks of P. caudatum and four of P. multimicronucleatum it was observed (total of 25 cases) that starved fragments do not regenerate either end of the cell up to the time of death though they survived long past the time required by feeding fragments to regenerate. Fragments which were prevented from regenerating by an initial period of starvation later regenerated when supplied with nourishment (69 cases). Only three fragments failed to recover normal form when fed, two showing conspicuous abnormality instead and one remaining unable to feed. Short anterior fragments (32 cases) and posterior fragments (four cases) which are nucleate but do not include the feeding organelles can neither feed nor regenerate either normal body shape or the oral structures. In seven cases it was found that when the oral region of whole animals was injured they could no longer feed and in six of these cases no mouth or gullet could be found. It is therefore suggested that organelles of ingestion cannot be regenerated when excised or damaged even though the normal site be present. These observations are considered to demonstrate that regeneration in Paramecium is entirely different in type from that of most protozoa in that it occurs only through feeding and subsequent growth if ingestive organs are already present in part at least. It does not occur by the remodeling of body shape, with the formation of oral primordia derived from more general cytoplasmic differentiations, as is the case in most ciliates. The original surprise of Balbiani in finding that his fragments of Paramecium did not regenerate like other ciliates is now explained.

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