PARAMAECIUM AURELIA AND PARAMAECIUM CAUDATUM 225 
modern systematic works as P. aurelia O. F. M. and P. cau- 
datum Ehrbg. 
Dujardin, in 1841, in his treatise on the Infusoria !, recognized 
but two species of Paramaecium as follows: 
PARAMECIE AURELIE.—Paramecium aurelia. 
Corps ovale oblong, arrondi ou obtus aux deux extrémités, 
plus large en arriére.—Long de 0, 18 4 0, 25. 
PARAMECIE A QUEUE.—Paramecium caudatum. 
Corps fusiforme, obtus ou arrondi en avant, aminci en 
arriére.—Long de 0, 22. 
His figures of the two species show clearly the characteristic 
form which he considered diagnostic. 
Various investigators, including Stein, and Claparéde and 
Lachmann, questioned the justification of considering these two 
forms as distinct species, basing their opinions, as had Ehrenberg 
and Dujardin, solely on external characters, and they united 
these two forms under one species, and applied Miiller’s original 
namie, P. aurelia. This union of aurelia and caudatum into one 
species was accepted by all the subsequent students of Paramae- 
cium, e.g., Balbiani, Biitschli, Engelmann, Gruber and Kolliker 
and consequently all the early literature on the conjugation of 
this infusorian, refers to the organism as P. aurelia, although it 
had but a single micronucleus. 
Maupas, in 1883, in his studies on the ciliates,’ wrote :— 
Tous les auteurs jusqu’ici ont décrit Paramecium aurelia comme ne 
possédant jamais qu’un nucléole d’assez grande taille et mesurant de 
Omm,005 4 Omm,008. C’est en effet la forme que l’on rencontre la 
plus fréquemment. Mais j’ai obsérve aussi de nombreux individus 
pourvus de deux nucléoles plus petits et de structure différente de la 
précedénte. Ils étaient de forme sphérique et composés d’un corpus- 
cule central opaque vivement coloré par les teintures et ne mesurant que 
Omm,003; enveloppé d’une couche corticale mesurant en diamétre 
Omm,005, claire et ne se colorant pas. 
12Histoire naturelle des Zoophytes. Infusoires, ete. Paris, 1841. Pp. 481-483, 
PIS 8; figs:'5, 65.7. 
8Contributions a l’etude morphologique et anatomique des Infusoires cilies, 
Arch. de zool. exp. et gen., (2), I, 1883, p. 660. 
