PARAMAECIUM AURELIA AND PARAMAECIUM CAUDATUM 227 
est fort possible que Claparéde et Lachmann aient eu raison, en considér- 
ant la forme caudatum comme plus typique que la forme aurelia. $i, 
en effet, on examine avec soin les dessins de O.—F. Miiller, on penche 
& croire que le vieux micrographe a vu et figuré la premiére seulement. 
En se conformant strictement au principe de la loi de priorité, ce serait 
done le nom aurelia, donné par Miller, qui devrait étre conservé & la 
forme fuselée. Mais, d’un autre c6té, Ehrenberg et Dujardin ont dis- 
tingué ce type et l’ont décommé caudatum. Si nous lui conservons la 
vieille dénomination aurelia, il devient impossible de transmettre le 
qualificatif caudatum & la forme qui, le plus souvent, est obtuse 4 
ses deux extrémités. Il faudrait alors eréer un nouveau nom. Je 
crois plus simple de conserver les dénominations d’ Ehrenberg. 
Since 1889, when Maupas" and Hertwig'®, in studies on conju- 
gation added further evidence for the distinction of the two forms, 
- they have been generally accepted as ‘good’ species. Calkins, 
however, again raised the question in 1906: ‘‘I personally believe 
that the slight differences that distinguish the two types of Para- 
mecium are not of specific value, and hold that P. caudatum 
should be regarded as a mere variant of P. aurelia.’’!7 He based 
this view chiefly on the following observations. One of a pair 
of ex-conjugants of P. caudatum, which he was studying by his 
well-known accurate culture methods, reorganized as P. caudatum 
and the other as P. aurelia, i.e., the latter had two small micro- 
nuclei, instead of one, and remained in this condition for about 
forty-five generations in pedigree culture, and then reverted to 
the caudatum type with one large micronucleus. While the 
aurelia phase existed, the rate ofedivision was comparatively 
slow, and when the caudatum phase was reassumed the rate of 
division immediately increased considerably. Calkins also con- 
sidered the relative size of the two forms, and the conjugation 
phenomena as described by Maupas and Hertwig, and concluded 
that these are not of such a character as to warrant their being 
considered diagnostic. . 
6 Le rajeunissement karyogamique chez les cilies, Arch. de zool. exp. et gen., (2), 
7, 1889. 
16 Ueber die Konjugation der Infusorien, Abh. kgl. bayr. Akad. d. Wiss. Miinchen, 
2, C1.°17, 1889. 
17Paramecium aurelia and Paramecium caudatum. Studies by the pupils of 
W. T. Sedgwick, 1906. 
