134 -A CENTURY Of PROGRESS IN THE NATURAL SCIENCES 



chen als vollkommene Organismen laid the foundation upon which the structure 

 of knowledge of the euglenids rests. Ehrenl^erg erected for them the family 

 Astasiaea, wliich he placed along with several other families, comprising uni- 

 cellular and colonial forms such as volvocines, dinoflagellates, desmids, diatoms, 

 and amoebae, in his "Polygastrica anentera," the gutless stomach animalcules. 

 Dujardin (1841) showed that the "Polygastrica anentera" were not perfect 

 miniature replicas of the Metazoa, pointing out among other things that the so- 

 called stomach of these beings was a vacuole. He proposed a system of classifi- 

 cation based primarily on the various means of locomotion. His third order (p. 

 270) comprised Infusoria ". . . pourvus d'un ou plusieurs filaments flagelli- 

 formes servant d'organes locomoteurs. — Sans bouche." It received a number of 

 flagellated forms such as monads, volvocines, euglenids, and dinoflagellates. By 

 uniting these organisms in a single group, Dujardin became the founder of 

 the assemblage for which Cohn (1853, p. 273) later proposed the name Flagellata. 



Siebold (1848, 1849) extended the observations of Dujardin and in con- 

 formity with Schleiden and Schwann's new cell theory pointed out for the first 

 time that the Infusoria of Ehrenberg were single-celled beings. He abandoned 

 Du jar din's group since he believed that the flagellated organisms were either 

 plants or animals and there were no intermediates. Siebold erected a class Rhizo- 

 poda for the nonflagellated (amoeboid) members of this complex and placed it 

 along with the amended class Infusoria (which included among others the eu- 

 glenids) in a major group for which he adopted (with altered circumscription) 

 the designation Protozoa of Goldfuss (1820, p. 57). Siebold excluded from his 

 group Protozoa organisms that were unable to change their body form through 

 contraction and expansion, such as the volvocines, desmids, and diatoms, which he 

 regarded as plants. He was inconsistent in this, however, for he retained the 

 peridinians as a family of animalcules in the Infusoria. 



Following Siebold's establishment of the unicellular nature of the Flagellata, 

 little of major importance to our knowledge of the group (as circumscribed by 

 Siebold) was published until the appearance of the papers by Cienkowski (1865a, 

 1865b, 1870), who made the first detailed observations on the life histories of 

 various members of the group and brought light and clarity into the chaotic state 

 of affairs as regards knowledge of the reproduction of these organisms. 



In 1878 appeared the first part of Stein's classical work on the natural his- 

 tory of the Flagellata. Stein regarded the Flagellata (including the Volvoca- 

 ceae), in agreement with Dujardin, as belonging to the Infusoria (that is, as 

 animals), since they possessed flagella, nuclei, and contractile vacuoles, appar- 

 ently overlooking the fact that a nucleus and a contractile vacuole had previ- 

 ously been shown to be present in the motile reproductive cells of certain typical 

 algae. He gave an excellent historical review of the advances in knowledge of 

 these organisms up to the time of his writing and his illustrations of many of 

 them still rank among the best that have been produced of the forms in question. 



Comprehensive treatises covering much the same field were published shortly 

 afterward by Kent (1880-1881) and Biitschli (1883-1887). Both these authors 

 also gave excellent reviews of the history of the group in the broad sense. 



In proclaiming that some of Ehrenberg's Infusoria were plants rather than 

 animals, Siebold (1848) started a long-continuing dispute as regards the nature 

 of many of the flagellated microorganisms. At first botanists were not particu- 



