38 INVERTEBRATE ZOOLOGY 



the typanosomes, but in structure, in habits, and in reactions 

 they seem to be more closely related to the bacteria. Treponema 

 pallidum, the spirochaete which causes syphilis, is one of the most 

 important representatives of this group. Some of the species 

 of the genus Spiroschaudinnia produce a disease in man known as 

 relapsing fever. 



In his "Biology of the Protozoa," G. N. Calkins (1926) rules 

 the spirochaetes out of the Protozoa, "as their main character- 

 istics place them much closer to the bacteria than to Protozoa. 

 Their transverse division and spore formation through coccoid 

 bodies are not duphcated amongst flagellated Protozoa, but are 

 distinctly Spirillum-like." 



Class Sarcodina 



The Sarcodina usually lack a true cell wall, though in many 

 instances skeletons or other protective coverings have been 

 developed. The cytoplasm is characteristically more fluid than 

 in other classes of Protozoa. The majority of Sarcodina are 

 floating forms tending toward spherical body shape, but creeping 

 forms attain flattened bodies or become cylindrical. 



Pseudopodia are the most characteristic feature of the Sar- 

 codina in spite of the extremely different appearances which these 

 structures may present in the various orders. In most instances, 

 pseudopodia serve both for locomotion and for the ingestion of 

 food. No less than four types of pseudopodia are generally 

 recognized by students of Protozoa: axopodia, my:xopodia, filo- 

 podia, and lobopodia. In the order named these represent 

 progressive modification from motile, ancestral flagella. Each 

 axopodium (Fig. 24 C) is provided with an axial filament arising 

 from a kinetic element in the endoplasm. The filament is 

 invested by a sheath of ectoplasm endowed with powers of 

 streaming back and forth along the filament. Thus structurally 

 there is very close agreement between an axopodium and a 

 flagellum. Myxopodia (Fig. 24 B) lack an axial filament but 

 possess a core of denser protoplasm. When they come in contact 

 they tend to fuse forming a mesh or network of cytoplasm 

 as in the Foraminifera. Filopodia lack all axial structures 

 and consist of a wholly homogeneous cytoplasm. Lobopodia 

 (Fig. 24 A), the form of pseudopodia encountered in Amoeba, 

 are the most transitory type. For their formation they are 

 dependent wholly upon the fluidity of the protoplasm. 



