BOOK FIRST. 



INFUSORIA AND RHIZOPODA. 



CLASSIFICATION. 



§3. 



The Infusoria, using this word \r\, a restricted sense, are far from being 

 the highly-organized animals Ehrenberg has supposed. In the first place, 

 on account of their more complicated structure, the Rotifera must be quite 

 separated from them, as has already been done by Wiegmann, Burmeister, 

 R. Wagner, Milne Edwards, Rymer Jones, and others. The same may 

 be said of the so-called Polygastrica. In fact, a great number of the 

 forms included under Closterina, Bacillaria, A^olvocina, and others placed 

 by Ehrenberg among the anenteric Polygastrica, belong, properly, to the 

 vegetable kingdom. Indeed, this author has very arbitrarily taken for 

 digestive, sexual, and nervous organs, the rigid vesicles, and the colored 

 or colorless granular masses, which are met with in simple vegetable forms, 

 but which are always absent in those low organisms of undoubtedly an 

 animal nature. Cell-structure and free motion are the only two character- 

 istics in common of the lowest animal and vegetable forms ; and since 

 Schwann '^' has shown the uniformity of development and structure of 

 animals and plants, it will not appear strange that the lowest conditions 

 of each should resemble each other in their simple-cell nature. As to 

 motion, the voluntary movements of Infusoria should be distinguished 

 from those which are involuntary, of simple vegetable forms ; a distinction 

 not insisted upon until lately. Thus, in watching carefully the motions of 

 Vorticellina, Trachelina, Kolpodea, Oxytrichina, &c., one quickly per- 

 ceives their voluntary character. The same is true of the power of con- 

 tracting and expanding their bodies. 



But in the motions of vegetable forms other conditions are perceived ; 

 and there is no appearance of volition in either change of place or form, 

 their locomotion being accomplished either by means of cilia, or other 

 physical causes not yet well understood. Cilia, therefore, belong to 

 vegetable as well as to animal forms, and in this connection it is not a little 

 remarkable that in animals they should be under the control of volition. 

 With vegetable forms these organs are met with either in the shape of 

 ciliated epithelium, as upon the spores of Vaucheria,'^-^ or as long, waving 

 filaments, as upon die earlier forms of many confervae,''" in which last can 



' Mikroskopische Untersucbunjen, he. Berlin, teurs des spores des Algues. Ann. des Sc. Nat. 

 1839 Botan. 1843, XIX. p. 266. PI. XI. fig. 29-30. 



* Thuret. Recherclies sur les organes locomo- ^ The same. PI. X. 



