Protozoa 249 



is no flagellum, but the body may be temporarily extended in 

 various directions. Such extensions, used for locomotion, are 

 called pseudopodia, which means false feet in Greek. Another 

 series, the Infusoria, moves by a great many relatively short 

 hair-like movable processes, called cilia. These differences are 

 not always clear; thus certain Infusoria lack the cilia when adult, 

 and the curious genus Deinamoeba has both flagella and pseudo- 

 podia. Nevertheless, in nearly every case the distinction is clear 

 enough, and the three groups can be recognized at a glance. There 

 is a strong tendency among the Protozoa to develop parasitic forms, 

 and this occurs independently in the different groups. Thus the 

 parasite which produces dysentery is one of the Sarcodina; that 

 which gives rise to sleeping sickness belongs to the Mastigophora. 

 There is, however, a special subphylum, Sporozoa, consisting 

 entirely of parasites, having usually no true organs of locomotion, 

 and characteristically reproducing by division into a multitude 

 of minute objects, the so-called spores. It is to this group that 

 the malaria parasites belong. 



Still another subphylum, the Mycetozoa or slime-molds, in- 

 cludes Protozoa adapted for life in air. They have been regarded 

 by many as plants, and are described in botanical works, but on 

 the whole they are best regarded as aberrant animals, genetically 

 unrelated to the fungi or other lower plants. They produce 

 spores, which give birth, in the presence of water, to swarm cells, 

 which are minute flagellate objects. These swim about and feed 

 on bacteria. After a time they join together and form a slimy 

 mass called the plasmodium, which may often be found on damp 

 logs. It is saprophytic, feeding on dead plant tissue. This 

 usually becomes dry, and forms a sporangium, sometimes of 

 considerable size. Thus the sporangium of Reticularia, found on 

 trees, grows to four or five inches in diameter, and may be taken 

 for a sort of puff-ball. From the sporangium come the spores, 

 and the life-cycle begins again. These Mycetozoa are very abun- 

 dant and varied in Colorado, where they have been carefully 

 studied by Sturgis and Bethel.* 



*If we regard the slime-molds as animals, the family-name Margaritidae, used inde- 

 pendently by Dollein and the writer in 191 I, cannot be employed, since the generic name on 

 which it is founded is a homonym. For a similar reason, the family name cannot be based on 

 Dianema. It remains only to use the name Prototrichiidae, based on Prototrichia Rost, though 

 this is not very closely related to the others. 



