ORGANIZATION OF THE FLAGELLATA. 



237 



The latter are at once most numerous, most highly developed, and 

 most manifestly animals, while the Flagellates recall in many ways 

 certain vegetable organisms, and often approach the unicellular Algae 

 so closely in structure and life-history, that a separation can only be 

 based on the decidedly animal mode of their nutrition. Many Fla- 

 gellata also resemble very closely the swarm-spores of certain Ehizo- 

 poda. 



Both groups include numerous parasitic forms, which infest both 

 the lower and higher animals, including man. 



Order I. FLAGELLATA. 



[Davaine, Art. ' ' Monadiens, " "Diet. sci. me*d.," 1874. R. L.] 



Stein, " Organisraus der Infusionsthiere," Abth. iii., 1878. 



Blitschli, " Beitrage zur Kenntniss der Flagellaten, " Zeitschr. f. wiss, Zool., Bd. xxx., 

 pp. 205 et seq., 1878. 



Dallinger and Drysdale, ' ' Researches on the Life-history of the Monads," Monthly 

 Micr. Journ., vols. x.-xiii., loc. div., 1873 to 1876. 



[Grassi, " Intorno ad alcuni protisti Endoparassitici," Atti Soc. Ital. sci. natur., vol. 

 xxiv., p. 47, 1882. R. L.] 



Infusoria of small size, and ivith but slight differentiation of the 

 body-parenchyma, so that the cortical layer and central mass are only 

 faintly contrasted, and a nucleolus can only rarely be distinguished. The 

 cilia are always confined to the anterior oral extremity, and are present 

 either singly or in small numbers. Sometimes there is also a ciliated 

 fringe surrounding the mouth like a collar, or running down the body in 

 the form of a longitudinal band. An anus seems always to be wanting. 



FIG. 117. Cercomonas muscce at different 

 stages. (After Stein.) 



FIG. 118. Bodo saltans. (After 

 Stein.) On the right an instance of 

 division. 



Of the numerous and often very wonderful and elegant forms of 

 flagellate Infusorians, we are here specially interested only in those 



