CLASSIFICATION 537 



particles of plants and animals. These may then be engulfed through 

 a mouth organ or they may simply be incorporated into the protozoan 

 protoplasm. Some of the latter, like ameba, possess as organs of 

 locomotion simple protoplasmic processes. These become attached 

 to small food particles, which then become incorporated into the 

 protoplasm by a flowing of the latter around the material intended 

 for food. When the latter are incorporated there is formed in the 

 engulfing protoplasm a food vacuole which secretes either acids or 

 alkalies and a digestive ferment of the peptic or tryptic type. From 

 the foodstuffs certain materials are extracted, others are stored as 

 reserve material (particularly oils and fats), and others again are 

 expelled as waste products. An exchange of gases is likewise kept 

 up by the protozoa, all of which show a more or less high degree of 

 irritability toward chemical and physical influences. 



Other protozoa, while existing under the same general laws of 

 metabolism, have by parasitism become adapted to a special mode 

 of life. They exist in the blood serum of higher animals (trypano- 

 somes) or they invade cells of the host (coccidia, plasmodium of 

 malaria of man and birds), and they then generally obtain their 

 food supply by osmotic processes. While the organs of locomotion 

 in the phylogenetic development of the protozoan races have evidently 

 been formed largely with the object of securing the food supply, they 

 have also been used extensively as the basis of the systematic sub- 

 division and classification of the species, etc., of the phylum protozoa. 



Classification. The classification as given in the last edition of 

 Calkins' Protozoology is followed, but reference is made only to those 

 subdivisions which embrace the parasitic and pathogenic protozoa 

 more fully considered in the following pages. 



The subphylum sarcodina is defined as protozoa showing no 

 connections with the bacteria, usually of simple structure and char- 

 acterized mainly by motile organs in the form of changeable proto- 

 plasmic processes, the pseudopodia. In this subphylum the subclass 

 ameba is of particular interest. It includes the more common 

 forms of rhizopods, with blunt or lobose pseudopodia, which do not 

 anastomose on touching one another. The protoplasmic body may 

 or may not possess a shell. 



The subphylum mastigophora comprises protozoa in which the 

 kinoplasm is concentrated in the form of one or more vibratile or 

 undulating motile processes called flagella, or in a kinetonucleus 

 which may lie inside or outside of the trophonucleus. This subphylum 

 comprises the very important flagellates, trypanosoma and herpeto- 

 monas and the less important cercomonas and trichomonas. 



The subphylum infusoria includes the protozoa in which the 

 motor apparatus is in the form of cilia, either simple or united into 

 membranes, membranelles or cirri. The cilia may be permanent or 

 limited to the young stages. With a micronucleus and a macro- 

 nucleus, reproduction is effected by simple transverse division or 



