PAPENFUSS: CLASSIFICATION OF THE ALGAE 135 



larly disturbed by these beings but in the course of time more and more of 

 them became involved in the argument. By 1850, zoologists had already con- 

 ceded that desmids and diatoms were plants but few of them were prepared to 

 relinquish the flagellates, including the Volvoeaceae. Haeckel (1866) attempted 

 to resolve the problem by erecting for the flagellates and various other micro- 

 organisms a kingdom Protista, which he considered intermediate between plants 

 and animals. Although the concept of a separate kingdom Protista was for a 

 time accepted by some biologists, it was later found untenable and has been 

 abandoned. 



A major advance toward an understanding of the morphology and the inter- 

 relationships of the flagellatas, with special reference to the euglenids, was made 

 by Klebs in 1883. Those biologists (Carter, 1856; Bcrgmann and Leuckart, 1852, 

 pp. 132-133; Cienkowski, 1870, p. 426; Hofmeister, 1867, p. 29; Schmitz, 1882, 

 p. 13, fn. 2) who had held that the euglenids, especially the green ones, were 

 algae had usually related them to the Palmellaceae. Since this family encom- 

 passed a very heterogeneous assemblage of organisms such as Protococcus (at 

 times referred to a separate family Protococcaceae), members of the Chlamydo- 

 monadaceae and Tetrasporaceae as now understood, and a number of other 

 types, Klebs decided to study the structure and reproduction of various mem- 

 bers of the Palmellaceae in order to obtain a sound basis for their comparison 

 with the euglenids. He found that the euglenids differed from the Palmella- 

 ceae in such important points as the structure of the limiting membrane of the 

 cell, the structure of the anterior end of the cell, the storage products, and the 

 method of division of the cell. Consequently, Klebs concluded that the Palmel- 

 laceae were typical algae and that the Euglenaceae constituted a sharply defined 

 group which bore no relationship to typical algae but perhaps was related, by 

 way of the Peranemeae, to the ciliates in the Infusoria. This possible alliance 

 was sufficiently remote, however, to justify recognition of the Euglenaceae and 

 Peranemeae as an assemblage distinct from the ciliates. He suggested that the 

 old designation Flagellata be employed for this group and was of the opinion 

 that probably the monads should also be retained in the Flagellata. In exclud- 

 ing the Euglenaceae from the algae, Klebs was not particularly perturbed by 

 their possession of chloroplasts since he erroneously believed that these struc- 

 tures were comparable to the cells of Zoochlorella in Paramaecium hursaria. 



Klebs (1883) also presented a systematic arrangement of the genera and 

 species of the family Euglenaceae, which served as the basis of later classifica- 

 tions of the assemblage. He divided the family into the two groups Euglenae 

 and Astasiae, the Euglenae receiving primarily photosynthetic forms whose cells 

 contained an eyespot and which went into a state of rest before dividing, and 

 the Astasiae receiving saprophytic forms which lacked plastids and an eyespot 

 and divided while in a motile state. 



Klebs believed that certain other organisms, typified by the genus Peranema, 

 represented a second natural group in the euglenid alliance. Among other dis- 

 tinguishing features, the members of this group possessed an oral apparatus. 



In a later monograph, Klebs (1892) maintained that the argument whether 

 the Flagellata were thallophj'tes or protozoa had lost significance and that it 

 was best to look upon them as a group intermediate between plants and ani- 

 mals and one from which various other microorganisms had evolved. At this 



