34 GENERAL ORGANIZATION OF THE PROTOZOA 



B. ORGANS OF LOCOMOTION OF PROTOZOA, AND CLASSI- 

 FICATION. 



As Dujardin ('41) early pointed out, the motile organs of protozoa 

 offer a natural basis for classification, which, with proper subdivisions, 

 is quite adequate to satisfy all of the requirements of a natural system. 

 Within the last year or so some confusion has arisen because of the 

 different forms an organism may assume at different periods of its 

 life history. Herpetomonas {Leishmania) donovani, the cause of kala 

 azar, for example, has an intracellular non-motile phase in addition 

 to a free-living, flagellated phase, and in such a form it is conceivable 

 that some difficulty might arise as to whether the organism should be 

 classified as a sporozoon or as a flagellate. Such exceptions, however, 

 do not offer insuperable difficulties, and may, indeed, serve a useful 

 purpose in pointing out the path of evolution which the organisms in 

 question have undergone. They do not in any way destroy the value 

 of the motile apparatus as a basis for classification. 



Dujardin outlined three of the four great divisions of the protozoa, 

 while the fourth, the Sporozoa, was named by Leuckart in 1S79. The 

 first group of protozoa was characterized by Dujardin as "animals 

 provided with variable processes" (pseudopodia); the second as 

 "animals provided with one or several flagelliform filaments" (flagella); 

 and the third as "ciliated animals." Gregarinida, belonging to the 

 fourth group, were the first protozoa to be regarded as single cells, 

 Kolliker ('45) regarding them as such. 



The finer subdivisions of these several groups are made chiefly 

 according to the variations in the structure of the motile organs, the 

 Sarcodina, for example, are here subdivided into two classes, the 

 Rhizopoda and the Actinopoda, according as the pseudopodia are 

 amorphous or ray-like. These .classes in turn are divided into sub- 

 classes, the former into Reticulosa, Mycetozoa, Foraminifera, and 

 Amebea, the latter into Heliozoa and Radiolaria. 



Some subdivisions of the protozoa deserve especial mention because 

 the organisms included, occupy an anomalous position in the scale of 

 living things. One such group, the Mycetozoa, is sometimes placed 

 as a group of rhizopods, sometimes as fungi. In their simplest forms 

 these organisms are minute cells with lobose pseudopodia, which are 

 soft and miscible and fuse upon coming together. Such fusions result 

 in great accumulations of protoplasm known as plasmodia, which may 

 assume a variety of shapes and may become so highly differentiated 

 as to resemble higher metaphytes much more than single celled 

 protozoa. Another such group, the Phytoflagellida, have long been 

 the subject of academic wrangling as to the boundary line between 

 animals and plants. Similarly, the Spirilloflagellata are today the 



