Vorticellina.] THE INFUSORIA. 251 



FAMILY XIII.— VORTICELLINA. 



These polygastric animalcules are provided with an 

 alimentary canal, the extremities of which are distinct, 

 though they approximate, in consequence of its curvature 

 (anopisthia). They have no lorica; when free, they are 

 solitary, but when attached to a pedicle they are social, 

 often assuming elegant remorse forms, like little trees, an 

 animalcule surmounting and terminating each branch or 

 pedicle. These clusters are produced by their imperfect 

 mode of self-division. 



The animal organization of this family is very distinct, 

 with the exception of vessels and nerves. All the species 

 possess numerous cilii ; those of Stentor are covered with 

 them ; others have them at the mouth ; they are mostly 

 disposed in the form of a wreath. By the vibratile action 

 of these, locomotion is effected. In some genera, as in 

 Vorticella, Carchesium, and Opercularia, longitudinal and 

 transverse muscles are seen. The polygastric nutritive 

 apparatus may be observed in all the genera, by feeding 

 them upon artificial colouring food. The course of the 

 alimentary canal has been observed in all the genera except 

 Trichodina and Urocentrum ; the mouth and discharging 

 opening, both lying in the same lateral cavity, have also been 

 demonstrated in all. The sexual system is hermaphrodite, 

 and self-division is known in all except Zoothamnium, 

 which is rare. In four genera the latter mode of propa- 

 gation is imperfect ; hence they form beautiful little tree- 

 like clusters. Another mode of propagation is observable, 



