Biological Studies (Classic Reprint) - Softcover

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Excerpt from Biological Studies

At the present time, when the subject of mutations and species is discussed on every hand, and when every eye is keenly on the alert for new evidence among animals and plants, a sudden transformation of one known species into another known species is of interest. Such an incident has recently come under my observation; a Paramecium caudatum became P. aurelia, and remained so for about 45 generations, when it reverted to P. caudatum. Apart from the facts of the change, which in itself is of obvious importance from the standpoint of cellular biology, the essential question to consider is whether these two species are sufficiently well defined to justify their separation. If not, then the experiments and the changes indicated have less bearing on the general problem of mutation than upon the problems of cell physiology. If they are sufficiently distinct, then we have in this incident an interesting case of mutation. I personally believe that the slight differences that distinguish the two types of Paramecium are not of specific value, and hold that P. caudatum should be regarded as a mere variant of P. aurelia.

Paramecium aurelia was the name given by Müller, in his general work on the Protozoa in 1773, to the ciliated organism which had been known as the "slipper animalcule." Several different species of Paramecium were created by Ehrenberg in 1838, and described in his work on the Infusionsthierchen. Most of these have been sifted out into other genera, and only three have remained, P. bursaria, P. aurelia, and P. caudatum. Paramecium caudatum and P. aurelia have been united into a single species by the majority of observers subsequent to Ehrenberg, on the ground that the differences upon which Ehrenberg had based his species were inadequate. The number of species was thus reduced to two, and the names used were P. aurelia and P. bursaria, the former having been given originally by Müller.

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