466 THE PROTOZOA 



cytoplasm distinct, which moved by means of pseudopodia ; but 

 it must be supposed that some of the pseudopodia very soon under- 

 went modifications which resulted in the acquisition of true flagella, 

 and thus arose at a very early stage of evolution the flagellula or 

 monad-form. In all probability these earliest monads were forms 

 with an amoeboid body, most nearly represented at the present 

 day by such forms as Cercomonas (Fig. 114) or the flagellulae of 

 Mycetozoa (Fig. 98). From such forms arose the Sarcodina and 

 their derivatives (Neosporidia) by loss of flagella and specialization 

 of the amoeboid form in the adult, and the Mastigophora and their 

 derivatives (Telosporidia, Infusoria) by specialization of the flagellar 

 apparatus combined with the acquisition of a cortex and loss of 

 amoeboid movement. 



If the foregoing phylogenetic speculations be accepted, it is clear 

 that in a natural classification of the Protozoa the Sporozoa must 

 be abolished as a class, and the two groups comprised in them 

 must either be raised to the rank of independent classes or dis- 

 tributed amongst the others the Telosporidia placed near the 

 Mastigophora, the Neosporidia near the Sarcodina. The primary 

 subdivision of the Protozoa, if it is to represent the first branching 

 of the ancestral stem, should be one which places on one side the 

 Mastigophora, Telosporidia (better Rhabdogenise), and Infusoria, 

 on the other the Sarcodina and Neosporidia (better Amcebogeniaa). 

 Beyond this point it is scarcely profitable at the present time to push 

 phylogenetic speculations farther. 



In conclusion, two groups of organisms require brief mention 

 the Spirochaetes and the Chlamydozoa since by many authorities 

 they have been referred to a position in or near the Protozoa. 



THE SPIROCHAETES. 



Under the name " Spirochaetes " are grouped a number of or- 

 ganisms, free-living or parasitic, with flexible bodies of slender, 

 thread-like form, concerning the nature and systematic position of 

 which a great deal of confusion has existed of recent years, due 

 chiefly to conflicting statements with regard to the facts of their 

 structure and methods of reproduction. The group comprises five 

 principal types, regarded each as of generic rank : 



1. Spirochceta sens, strict., a name given by Ehrenberg in 1833 

 to a relatively large, free-living form, S. plicatilis. Other species 

 of the genus have been described. For a full account, see Zuelzer 

 (904). 



2. Cristispira, a name proposed by Gross (897) for a number of 

 species parasitic in the digestive tract or crystalline style of Lamelli- 

 branch molluscs, and characterized by the possession of a crest or 



. 



