ties with Protomyxa, and with the Flagellata, but is more 

 highly differentiated ; while some of the Cilioflagellata (e.g., 

 Peridinium) shew such striking resemblances to some of the 

 lower plants that it is a question with some biologists 

 whether or not they belong to the animal series. But the 

 resemblances are really not surprising when we consider the 

 close relationship between the lower Infusoria and the Proto- 

 phyta. The common Protomyxa-like ancestor is not far 

 removed from either of them. 



In passing up to the higher Infusoria, we find that 

 the Holotricha {e.g., Paramoecium) — where besides internal 

 differentiation, the body has acquired a uniform covering of 

 cilia — are most nearly in the direct line of development {i.e., 

 are most nearly allied to the probable ancestral forms), 

 and may be regarded as the central group of the Ciliata. 

 The Hypotricha, the Heterotricha, and the Peritricha, 

 are more or less divergent groups, in which the cilia do not 

 form a uniform coating, and they may be conveniently 

 represented as being at the ends of side branches from 

 ancestors of the Holotricha. The Peritricha {e.g., Vorti- 

 cella) are probably further removed from the main line 

 than any of the others. The Opalinida, a small group 

 of parasitic Infusoria, found in the intestine of some 

 Amphibia, may be regarded as having degenerated from the 

 Holotricha, which they resemble in the arrangement of their 

 cilia. 



The Tentaculifera (or Suctoria, e.g., Acineta) are a rather 

 isolated group, the exact relations of which are difficult to 

 determine. Saville Kent traces them back to a point on the 

 main axis of the Protozoa, near to Amoeba, but it is more 

 probable that they have diverged from the stem of the 

 Infusoria, distinctly below the Ciliata, as shown in the table. 

 They are placed on a long side branch, which does not 

 rise much in its course. This indicates that they are 



