i8 ZOOLOGY FOR MEDICAL STUDENTS chap. 



" sickness " is caused by an abnormal increase in number of the amoeboid 

 and other organisms which prey upon the nitrifying bacteria, and that 

 the " cure " is brought about by the kiUing off in turn of these organisms 

 so that the more highly resistant bacteria are able to multiply till they 

 again reach their normal numbers. 



PROTOZOA 



SCHEME OF CLASSIFICATION 



L Sarcodina. 



A. Rhizopoda. 



I, Amoebaea. 2, Foraminifera. 



B. Actinopoda. 



3, Heliozoa. 4, Radiolaria. 



IL Flagellata. 



III. Sporozoa. 



A. Telosporidia. 



I, Gregarinida. 2, Coccidia. 3, Haemospondia. 



B. Neosporidia. 



4, Cnidosporidia. 5, Sarcosporidia. 6, Haplosporidia. 



IV. CiLIATA. 



I, Holotricha. 2, Heterotricha. 3, Hypotricha. 4, Peri- 



tricha. 

 Appendix to Ciliata — Acinetaria. 



I. SARCODINA 



Amoeba is a characteristic example of the main sub-division or phylum 

 of the Animal Kingdom called Protozoa because its members come first 

 in order of simplicity of obvious structure. This phylum includes a vast 

 number of different genera which when compared together and classified 

 are found to fall naturally into certain sub-groups the more important 

 of which are mentioned in the scheme given above. Amoeba itself is 

 placed with a number of its allies in the small group Amoebaea, character- 

 ized above all by the blunt pseudopodia (lobopods) which do not show 

 any tendency to fuse with one another. Two interesting examples of 

 this group are the genera Arcella and Difflugia, both common in fresh- 

 water pools. These, unlike Amoeba which is naked, shelter their bodies 

 within a portable house or shell, only the pseudopodia projecting 

 beyond its opening. In Arcella the shell is composed entirely of 



