in the evolution of higher organisms, both 

 plants and animals (Fig. 29-11). 



In addition to the many free-living species, 

 there are a few parasitic Mastigophora, and 

 some of these, especially the trypanosomas, 

 are important medically. The two forms of 

 African sleeping sickness, 2 both very serious 

 ailments, are caused, respectively, by Trypa- 

 nosoma gambiense (Fig. 32-3) and Trypano- 



i 



Fig. 32-3. Trypanosoma gambiense, a human blood 

 parasite, which causes one form of African sleeping 

 sickness. Four flagellated specimens can be seen 

 among the red blood cells. (Copyright, General Bio- 

 logical Supply House, Inc.) 



soma rhodesiense, which are injected into the 

 human blood stream by the bite of the tsetse 

 fly. Also two disfiguring diseases, endemic in 

 certain Asiatic and Mediterranean areas, 

 namely kala azar and Oriental sore, are 

 caused by tissue-invading flagellates of the 

 genus Leishmania. A sizable number of other 



2 African sleeping sickness should not be confused 

 with encephalitis, which also may be called "sleeping 

 sickness." Encephalitis is one of the virus diseases. 



The Animal Kingdom - 627 



trypanosomes occur as blood parasites in 

 various vertebrate animals. Two cattle dis- 

 eases of the Orient, surra and nagana, are 

 caused, respectively, by Trypanosoma evansi 

 and Trypanosoma brucei. Both of these are 

 transmitted by the tsetse fly, from local game 

 animals, especially antelope, which also har- 

 bor the parasites. Trypanosoma lewisi, trans- 

 mitted by fleas, is often found in the blood 

 of rats; and various other Trypanosoma, 

 transmitted by leeches, have been found in 

 the blood streams of various fish, amphibians, 

 and reptiles. 



The Ciliophora (Fig. 32-4). As the name 

 Ciliophora denotes, all members of this class 

 possess cilia. The group, however, is a diverse 

 one, which is divided into two subclasses: 



1. The Ciliata are forms that possess cilia 

 during all (active) stages of the life 

 cycle. 



2. The Suctoria are forms that are ciliated 

 during an early stage, but are noncili- 

 ated later. The adult suctorian, in fact, 

 is a sedentary animal. It fastens itself 

 to the substratum and feeds by means 

 of suction tentacles (Fig. 32-4, Podo- 

 phyra). 



The Ciliata. Although Paramecium, un- 

 doubtedly, 

 tive, there 



Ciliata that can be found in fresh, salt, and 

 brackish waters, especially in quiet spots, 

 where strong currents and heavy waves are 

 absent. 



Most ciliates display a unique feature. 

 Each cell possesses two types of nuclei — one 

 (or more) micronucleus, and one (or more) 

 macronucleus (Fig. 7-3). This differentiation 

 seems to represent a division of nuclear func- 

 tions. The micronucleus, apparently, deter- 

 mines the hereditary characteristics of the 

 species and transmits these to the next gener- 

 ation; whereas the macronucleus is more con- 

 cerned with metabolic processes in the cell. 

 However, nuclear reorganization may occur 

 periodically. At such times a new macronu- 

 cleus is formed from one of the micronuclei. 

 In Paramecium, for example, nuclear reor- 



is the most familiar representa- 

 is a very rich variety of other 



