22 



INTRODUCTION TO THE PROTOZOA 



Side of the mother and then grows to full 

 size. 



Internal budding or endodyogeny has 

 been described in Toxoplasma and Bes- 

 noitia. Two daughter cells are formed 

 within the mother cell and then break out, 

 destroying it (Goldman, Carver and Sul- 

 zer, 1958). 



Several types of sexual reproduction 

 have been described, but only two occur 

 in parasitic protozoa. In conjugation, 

 which is found among the ciliates, two in- 

 dividuals come together temporarily and 

 fuse along part of their length. Their 

 macronuclei degenerate, their micronu- 

 clei divide a number of times, and one of 

 the resultant haploid pronuclei passes 

 from each conjugant into the other. The 

 conjugants then separate, and nuclear re- 

 organization takes place. 



In syngamy, two gametes fuse to form 

 a zygote. If the gametes are similar in 

 appearance, the process is called isogamy; 

 if they are different, it is anisogamy, the 

 smaller gamete being the microgamete 

 and the larger one the macrogamete. The 

 gametes may be produced by special cells, 

 the microgametocytes and macrogamet- 

 ocytes, respectively. These are also 

 sometimes called gamonts. The zygote 

 may or may not then divide by multiple 

 fission to form a number of sporozoites. 

 The process of gamete formation is known 

 as gametogony. It may differ in different 

 groups, and will be described in the ap- 

 propriate places below. 



Some protozoa form resistant cysts 

 or spores. A cyst results from the for- 

 mation of a heavy wall around the whole 

 organism. Spores are produced within the 

 organism by the formation of heavy walls 

 around a number of individuals which have 

 been produced by multiple fission or other- 

 wise. This process, known as sporogony, 

 ordinarily follows syngamy. Each spore 

 may contain one or more individual organ- 

 isms or sporozoites. 



The vegetative, motile stage of a 

 protozoon is known as a tropliozoite. 



HISTORY 



The first person to see protozoa was 

 the Dutch microscopist, Antony van Leeu- 

 wenhoek (1632-1723). He used simple 

 lenses which he ground himself and which 

 gave magnifications as high as 270 times. 

 His letters to the Royal Society are a 

 classic of biology. Between 1674 and 1716, 

 Leeuwenhoek described many free-living 

 protozoa, among them, according to Dobell 

 (1932), being Euglena, Volvox and Vorti- 

 cella. Huygens in 1678 was the first to 

 describe Paramecium. Classic work on 

 free-living protozoa was done by O. F. 

 Milller (1786), Ehrenberg (1830, 1838) and 

 Dujardin (1841). 



The first parasitic protozoon to be 

 discovered was Eimeria stiedae; Leeuwen- 

 hoek found its oocysts in the gall bladder 

 of an old rabbit in 1674. Later, in 1681, 

 Leeuwenhoek found Giardia lamblia in his 

 own diarrheic stools, and in 1683 he found 

 Opalina and Nyctotherus in the intestine of 

 the frog. 



The first species of Tricfiomonas, 

 T. tenax, was found by O. F. Miiller in 

 1773 in the human mouth; he named it 

 Cer carta tenax. Donne found T. vaginalis 

 in the human vagina in 1837, and Davaine 

 found Trichomonas and Chilomastix in the 

 stools of human cholera patients in 1854. 



The first trypanosome was discovered 

 in the blood of the salmon by Valentin in 

 1841, and the frog trypanosome by Gluge 

 and Gruby in 1842. Lewis found the first 

 mammalian trypanosome, T. lewisi, in the 

 rat in 1878. Evans discovered the first 

 pathogenic one, T. eva>isi, in 1881 in India, 

 where it was causing the disease known as 

 surra in elephants. Bruce discovered T. 

 brucei in Africa in 1895 and described its 

 life cycle and transmission by the tsetse 

 fly in 1897. In 1902, Dutton discovered 

 that African sleeping sickness of man was 

 caused by T. gambiense. Leishmania 

 tropica was first seen by Cunningham in 

 India in 1885 and was first described and 

 identified as a protozoon by Borovsky in 

 Russia in 1898. Leishman and Donovan 

 independently discovered Leishmania 

 donovani in India in 1903. 



