CHAPTER XXVII 



THE PROTOZOAN SUBGROUPS. DISEASES DUE TO 

 PROTOZOA 



Class I. Rhizopocla. Protozoa (p. 311). 



The Protozoa of this group lack permanent structures for locomotion 

 and nourishment, these functions being performed by the undifferen- 

 tiated protoplasm. For this reason they are considered to be the lowest 

 in position of the Protozoa. The class name — Rhizopoda — has ref- 

 erence to the extension of the cytoplasm in root-like processes or feet, — 

 the pseudopodia or false feet. It is in this manner that the anmial flows 

 over and engulfs its food, the movements serving for locomotion as well. 

 This type of locomotion is known as ameboid, it having been first 

 accurately studied in the Ameba. It differs from that of higher Pro- 

 tozoa in that it is not accomplished by constant cell organs, as ciha and 

 fiagella. A pseudopodium is formed when the cytoplasm streams to a 

 point of the body, the process extending more or less beyond the gen- 

 eral body surface; the body may then be drawn after it or appear 

 to flow into it, the protrusion disappearing and new pseudopodia being 

 formed at other points. By repetition of this process a slow change 

 in the position of the organism occurs, and if particles of nourish- 

 ment are encountered in such wandering they are engulfed by 

 the cytoplasm within which they become surrounded by a certain 

 amount of liquid, presumably of a digestive nature, to form the food 

 vacuole. 



The form of the pseudopodia varies, and this serves as a factor in the 

 separation of the rhizopods into different groups. In the Ameba (Fig. 

 168) they are thick and finger-like, while in certain other forms they are 

 of such delicacy as to appear like fine threads. 



Reproduction in Rhizopoda may be accompanied with the formation 

 ■of flagellate spores, the ameboid method of motility being exchanged 

 for that of the flagellated Protozoa. In this stage the body becomes 

 oval and the flagellum develops at the end containing the nucleus, 

 where it persists during the spore stage. 



The parasitic Rhizopoda belong with the order Lobosa which is the 

 only one considered here. The characteristics of this group have been 

 sufficiently referred to in the description of the type genus Ameba 

 (p. 312). There are but few parasitic species known, and these are 

 included in the two genera Ameba and Entameba. 



