204 THE PROTOZOA 



part becomes drawn out into the long contractile stalk, while the 

 ciliated condition, as represented by Trichodina, is again brought 

 about in Vorticella, when the latter breaks away from its stalk, 

 develops a ciliated band in the posterior region, and swims freely 

 about. The ciliated band is homologous with the posterior ring of 

 Lichnophora and the attaching disk of Trichodina, while the adoral 

 zone of cilia conforms to the typical left-handed spiral of the remain- 

 ing ciliates, when looked at from the same morphological point of 

 view. In Gerda, the peristomial region has degenerated, while the 

 ciliated disk remains as the organ of locomotion. 



Returning now to the origin of the Ciliata as a group, quite another 

 view has been maintained by a number of observers, the essential 

 point of which is that the Ciliata are connected with the Sarcodina 

 through the Suctoria, the tentacles in the latter being regarded as 

 modified pseudopodia. This view was apparently first suggested by 

 Stein ('54) when he included the Heliozoa and the simpler forms of 

 Suctoria in the genus Actinophrys. The assumption was taken up 

 seriously by Maupas ('81), who held that through the Suctoria, the 

 Ciliata were derived from the Sarcodina, and Penard ('90) accepted 

 the same view in regarding Actinolophus capitatus as a connecting 

 link between the two groups. Claparede and Lachmann were the 

 first to deny the connection of Ciliata and Rhizopoda, but made the 

 even more improbable assertion that the Suctoria are derived from 

 the Flagellidia through forms like Synctypta volvox. The close rela- 

 tion of the Suctoria and the Ciliata was brought into prominence 

 through Stein's famous, though erroneous, Acineta-theory, in which 

 the Suctoria were supposed to be young forms of Ciliata. The con- 

 nection between the two was, however, first put on a substantial basis 

 by the discovery of the ciliated embryos of the Suctoria, a connection 

 which was early accepted by students of the Protozoa, and which was 

 greatly emphasized by the discovery that, like the Ciliata, the Suctoria 

 have macro- and micronuclei. 



At the present time it is almost universally held that the Suctoria 

 are offshoots of the Ciliata, although the opposite view is maintained 

 by some observers, who,' with Entz ('79, '82), consider the Ciliata as 

 permanent forms of the ciliated embryos of Suctoria. Entz himself 

 regards the matter as insoluble, and believes that the evidence is 

 about equally balanced. A number of cases certainly gives strength 

 to Entz's position, for many of the Enchelinidae, in addition to their 

 cilia, have distinct tentacular processes (Ileonema, Mesodinium, 

 Actinobolus, etc., Fig. 115). 



Actinobolus, discovered by Stein, and more recently examined by 

 Entz, has long tentacle-like threads evenly distributed about and 

 between the cilia (Fig. 100). They can be lengthened or shortened 



