392 ann bishop 



1. Historical. 



The genus Spirostomum was first mentioned by Ehrenberg, 

 but no definition nor description was given. Its systematic 

 position and the question of the number and identity of the 

 species contained in it was a subject for discussion for many 

 years. Later, Dujardin (7) gave a very satisfactory description 

 of the genus in the following words : 



' Corps cylindrique tres-allonge et tres-flexible, souvent 

 tordu sur lui-meme, convert de cils disposes suivant les stries 

 obliques ou en helice de la surface ; avec une bouches situee 

 lateralement au dela du milieu, a I'extremite d'une rangee de 

 cils plus forts.' 



He recognized, however, only Spirostomum a m b i g u u m 

 as a true species. 



It is to Dr. Stein (28) that we are indebted for a comprehen- 

 sive and beautifully illustrated description of the genus, 

 together with a detailed account of the vicissitudes of nomen- 

 clature through which it had passed since its discovery by 

 Ehrenberg. Stein recognizes two species of Spirostomum, 

 S. ambiguum (Ehrenberg) and S. teres (Claparede et 

 Lachmann) (5). Previously Perty (24) had included another 

 form in the genus, and to it he gave the name S. semi- 

 virescens. His observations, which were founded on a 

 single specimen, are regarded by Stein as being of too 

 superficial a nature to justify the creation of a new species. 

 He believed it to be merely a variety of Spirostomum 

 ambiguum. 



Penard (23) recognizes S. ambiguum and S. teres 

 as true species, and to these adds S. filum. This latter, 

 although described by Ehrenberg as Uroleptus filum, 

 was placed tentatively in the genus Spirostomum by Biitschli (3) 

 and Claparede et Lachmann. Stein does not classify it among 

 his species. None of the above workers, with the exception 

 of Ehrenberg, had seen it personally, but has relied upon 

 Ehrenberg's figures for their data. Penard has actually seen 

 it, and feels quite certain that it justifies the position he has 

 given it as a third species of the genus Spirostomum. 



