Abstract
The work of Jennings1 affords much evidence that, in Paramecium, morphological differentiations, which are hereditary, do not arise in a line reproducing vegetatively. As a result, selection is powerless to isolate hereditarily different strains among the descendants of a single cell. On the other hand, the same author2 has shown that in the uniparental reproduction of a rhizopod, Difflugia corona, the number and length of the spines on the test, as well as other morphological characters, become differentiated in the descendants of a single individual; and that by selection it is possible to isolate many hereditarily different strains.The effectiveness of selection in regard to what may be termed a physiological character has not been tested in Paramecium, but Middleton3 has undertaken this in a study of the fission rate of another ciliate, Stylonychia pustulata. This author found that “by opposite selection, through more than 150 generations, of small individual variations occurring among the progeny of ...
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