FLAGELLATA I I 9 



an increased toleration and resistance from one generation or 

 cycle to another. 



As we noted above (p. 40), the study of the Flagellates has 

 been largely in the hands of botanists. After the work of Biitschli 

 in Bronn's Thier-Reich , Klebs 1 took up their study ; and the prin- 

 cipal monographs during the last decade have appeared in Engler 

 and PrantFs Pflanzenfamilien, where Senn 2 treats the Flagellates 

 generally, Wille 3 the Volvocaceae, and Schiitt the " Peridiniales " 

 or Dinoflagellata ; 4 while only the Cystofiagellata, with but two 

 genera, have been left to the undisputed sway of the zoologists. 5 



Among this group the majority are saprophytes, found in 

 water containing putrefying matter or bacteria. The forms so 

 carefully studied by Daliinger and Drysdale belong to the genera 

 Boclo, Cercomonas, Tetramitus, ITonas, and Dallingeria. Many 

 others are parasites in the blood or internal cavities of higher 

 animals, some apparently harmless, such as Trichomonas vaginalis, 

 parasitic in man, others of singular malignity. Costia necatrix, 

 infesting the epithelial scales of fresh-water fish, often devastates 

 hatcheries. The genus Trypanosoma, Gruby, contributes a 

 number of parasites, giving rise to deadly disease in man and 

 beast. 6 T. lewisii is common in Rodents, but is relatively harm- 

 less. T. evansii is the cause of the Surra disease of Ruminants 

 in India, and is apparently communicated by the bites of " large 

 brown flies " (almost certainly Breeze Flies or Tabanidae, Vol. VI. 

 p. 48 1). T. hrucei, transferred to cattle by the Tsetse Fly, Glossina 

 morsitans (see Vol. VI. Fig. 244, p. 513) in Equatorial Africa, is 

 the cause of the deadly Nagana disease, which renders whole 

 tracts of country impassable to ox or horse. Other Trypanosomic 

 diseases of animals are, in Algeria and the Punjab, " dourine," 

 infecting horses and dogs ; in South America, Mai de Caderas 

 (falling-sickness), an epidemic paralysis of cattle. During the 

 printing of this book, much additional knowledge has been gained 

 on this genus and the diseases it engenders. The Trypanosomic 



1 In Z. iviss. Zool. lv. 1893, p. 353. 2 1. Teil, Abt. 1. a, 1900. 



3 In the Chlorophyceae, 1. Teil, Abt. 2, 1897. 4 1. Teil, Abt. 1. b, 1896. 



5 Besides the above, Dangeard, in various papers in his periodical Le Botaniste, 

 has treated of most of the groups, and Raoul France has monographed the Poly- 

 tomeae in the Jahrb. wiss. Bot. xxvi. 1894, p. 295, and Dill the genus Chlamy 

 domonas, etc., its closest allies, in oj). eit. xxviii. 1895, p. 323. 



6 For a detailed abstract of our knowledge of Trypanosoma and its allies up to 

 Feb. 1, 1906, see Woodcock, "The Haemoflagellates," in Quart. Journ. Micr. Sci. 

 1. 1906, p. 151. 



