MASTIGOPHORA : FLAGELLATA. 841 



holozoic, saprophytic, or, when chromatophores are present, holophytic. Re- 

 production by simple binary fission in the motile condition ; or in the encysted 

 state, when it may be simple or continued, giving rise to a few or to numerous 

 small individuals. Conjugation frequent, the conjugating individuals being 

 either similar or dissimilar. Solitary or colonial. Freshwater, marine, in 

 decaying infusions ; rarely parasitic. 



The number of forms included in the Mastigophora is great. The 

 class may be subdivided into four sub-classes, the Flagellata, Chonano- 

 flagellata, Dinoflagellata and Cystoflagellata, the mutual relations of which 

 are uncertain. 



i. Flagellata. The members of this sub-class are characterised by 

 the possession of one or more vibratile flagella. The body is usually 

 more or less elongated and monaxial, sometimes asymmetrical, sometimes 

 bilaterally symmetrical either in shape or arrangement of parts ; con- 

 tractile in some instances, in others more or less amoeboid. A well- 

 developed cuticle may be present, or a membranous or gelatinous 

 envelope. 



The amoeboid condition is most strongly developed in the Monadina 

 Rhizomastigina. The pseudopodia are either simple or branched digitiform 

 processes (Mastigamoeba}, or radiant and Heliozooid in aspect (Dimorpha, 

 Ciliophrys, ? Actinomonas], coexisting with one or two flagella, except in 

 the two last-named. They may be partially retracted in Mastigamoeba, 

 wholly in Ciliophrys and Dimorpha. An amoeboid condition, especially of 

 the posterior region of the body, is apt to occur in some other Flagellata, 

 e. g. Cercomonas. The flagella vary in length, thickness, relative size, number, 

 and disposition. When only one or two they are restricted to the anterior 

 pole of the body. And in Heteromastigoda one of them the pulsellum 

 (gubernaculum of James Clark) is large and bent backwards beneath the 

 body. An undulatory membrane is found in some parasites, e. g. Trypano- 

 soma, in which it extends along one side of the body. A thick layer of 

 exoplasm is present in Mastigamoeba, and the anterior extremity of the 

 body is in some cases formed of clear protoplasm free from chromato- 

 phores, &c. As a rule, however, no distinction into layers is recognisable. 

 A circulation of the protoplasm has been seldom observed ; its vacuolation 

 is rare and perhaps pathological 1 . 



A cuticle is absent in the simpler Monadina, Iso- and Hetero-masti- 

 goda, hence the possibility of an amoeboid condition ; but when the out- 

 line of the body is fixed it is present. It is best developed in some 

 Euglenoidea where it is hyaline, homogeneous, obliquely or longitudinally 



1 Mastigamoeba aspera has frequently delicate hair-like processes at its posterior end, such as 

 occur in Amoeba, &c. Its surface is covered with very small rod-like bodies of uncertain nature, 

 whether processes of the body or a coat of adherent Bacteria, very similar to what are seen in 

 Deinamoeba. 



