CLASSIFICATION OF THE MAIN SUBDIVISIONS 463 



Hartmann (892) recognizes six classes of the Protozoa : Class I., the Sarco- 

 dina, including four subclasses namely, Rhizopoda, Heliozoa, Radiolaria, 

 and Mycetozoa ; Class II., the Cnidosporidia, including Microsporidia, Sarco- 

 sporidia, Myxosporidia, and Actinomyxidia ; Class III., the Mastigophora, 

 including the Rhizomastigina, Protomonadina, Binucleata, Chromomonadina, 

 Euglenoidea, and Phytomonadina, the order Binucleata including the Haemo- 

 flagellates and the Hsemosporidia with the exception of the hsemogregarines ; 

 Class IV., the Telosporidia. including the grcgarines, coccidia, and haemo- 

 gregarines ; Class V. ? the Trichonymphida ; Class VI., the Infusoria. With 

 regard to this classification, the order Binucleata has been dealt with at 

 length above ; it only remains to say that the isolated position given to the 

 Trichonymphida appears to express the defective state of knowledge con- 

 cerning the affinities of these peculiar parasites, rather than their true taxo- 

 nomic importance. 



A number of radical changes in the classification of the Protozoa are pro- 

 posed by Awerinzew (890). With Hartmann he unites the Haemoflagellatcs 

 and Haemosporidia in an order Binucleata to be placed in the Flagellata. 

 The class Sporozoa is to be entirely abolished. The order Amcebina 

 (Amcebsea) is removed by him entirely from the Sarcodina, which will then 

 comprise only the Foraminifera and some Heliozoa. The Amcebina are to be 

 put with the Flagellata as the Amceboflagellata, a group from which all other 

 Protozoa are supposed to have arisen, and from which the Amcebina branch 

 off in one direction, the Flagellata and Dinoflagehata in another. The gre- 

 garines are believed by Awerinzew to be connected on the one side with the 

 Amcebina, on the other with the Coccidia. In the Neosporidia, the Sarco- 

 sporidia are regarded as allied to Flagellata ; the Myxosporjdia, Microsporidia, 

 and Actinomyxidia, are considered not to be Protozoa at all ; the. Haplo- 

 sporidia are to be placed provisionally as an independent group taking origin 

 from Amcebina. For the Infusoria, it is suggested that they take origin from 

 amoeboflagellate ancestors rather than from true Flagellata. 



The object of what is termed a natural as opposed to an artificial 

 system of classification is to endeavour to express by the arrange- 

 ment of the groups the affinities of the living organisms concerned, 

 and more especially the genetic relationships of one to another on 

 the theory of evolution that is to say, on the assumption or belief 

 that forms now existing are descended from older ancestral forms, 

 and that any two existing forms are descended from a common 

 ancestral form more or less remote, according as the two existing 

 forms in question have diverged more or less widely from one another. 

 The foundation of a natural classification is therefore the phytogeny 

 of the groups dealt with that is to say, their pedigrees and lines 

 of descent, so far as they can be traced. Phylogeny must, however, 

 always be a matter of speculation, and to a large extent of personal 

 opinion, rather than of direct observation. It is only possible to 

 infer from the study of existing species what the ancestral forms 

 may have been like, since it is unnecessary to point out that no 

 form can be the ancestor of another species existing at the same 

 time. The most that can be said of two co-existing species is 

 that one of them may be believed to have diverged much less in 

 its characters from the common ancestral form than the other. 

 When, therefore, a given form is said to have an amoebic or a cer- 

 comonad ancestry, it is not intended to imply by that statement 



