Natural Ilistorij of the Vorticellje. 109 



himself and by Clapar^de and Lachmann. The limits which 

 he and his successors had at first widened have been again 

 contracted by Stein himself nearly within the original bounds, 

 as he has again separated the Ophnjdinahom the Vorticellce^ , 

 and accepted their right, first recognized by Ehrenberg, to 

 form a carapaced family side by side with the naked bell- 

 animalcules. He has also dissolved the union of the genus 

 OjJcrcularia with Ejnstylis made by Claparcde and Lachmami, 

 and raised the former, as was done by Ehrenberg, to the rank 

 of an independent genus. On the other hand, he has sepa- 

 rated Urocentrnm^ like Claparfede and Lachmann, but on the 

 grounds of a more accurate investigation than they had made — 

 and also Tricliodina^ which had hitherto remained combined 

 with the Vorticellce^ but differs from them in many essential 

 points, especially by the possession of a peculiar adherent 

 apparatus at the hinder end of the body, by the constant ab- 

 sence of a posterior circlet of cilia and of a protrusible and 

 retractile rotatory organ, &c., so that at first Stein even 

 ascribes to the TrichodincB tlie rank of a distinct family on 

 account of these peculiarities!, although subsequently he 

 arranges them as a genus of the newly formed family of the 

 Urceolarina. As new members, the genera Scyphidia and 

 Gerda, already introduced by Claparcde and Lachmann, are 

 accepted, and to these the genus Astylozoon^ discovered by 

 EngelmannJ, is added : it is characterized by the possession of 

 two springing-bristles, situated at the posterior end, in place 

 of a stem. 



Thus it comes to pass that, after all these changes, the pre- 

 sent systematic constitution of our family (with the above-men- 

 tioned natural exception of the Stentors) is once more nearly 

 the same as when it was founded by Ehrenberg. The genera, 

 also, have again been brought back to their original number, 

 namely eight; and these, after the alterations above indicated, 

 are : — Vorticella, Carchesium, Ejnstylis, Zoothamnium^ Oper- 

 cidaria^ 8cypMdia^ Gerda, and Astylozoon. 



The characters of the family thus united, as they have been 

 developed or, rather, have gradually acquired a sharjier pro- 

 minence in the way above described, may now be summed up 

 in the following points : — In the first rank we must place the 

 position of the mouth and anus in a common cavity in the 

 bottom of the first section of the nutritive tube, the so-called 

 vestihuhj which was correctly recognized and indicated as a 

 primary character by Ehrenberg. Next to this comes the 



* Der Organismus der Infusionsthiere, ii. p. 168. 



t Der OrganiRmus <\vy Inf. ii. p. 1 10. 



\ Zeitschr. fiir wiss. Zool. xi. p. o8i), pi. 31. figs. 15,10. 



