226 CLASSIFICATION OF ANIMALS 



side the capsule is another layer of protoplasm which contains large 

 quantities of a gelatinous secretion. Besides the central capsule there is a 

 skeleton, usually of silica, composed of radial spines and concentric shells. 

 This skeleton is often of a very intricate and beautiful design. The pseu- 

 dopodia are slender and branching and are sometimes supported by a 

 slender axial filament. The Radiolaria are marine. 



511. Class II. Mastigophora. The Mastigophora are dis- 

 tinguished by the flagellum, a whip-like vibratory appendage 

 by which locomotion is effected. There may be two or four or 

 even a circlet of these flagella but more often there is only one. 

 Flagella also occur in other groups of animals and also in plants 

 but only as temporary structures. In the Mastigophora they 

 are always present during the active life period of the organism. 

 The body has usually a definite form though it is often capable 

 of great contortion. There is a nucleus and a contractile 

 vacuole. The class may be divided into three sub-classes, Flag- 

 ellata, Dinoflagellata and Cystoflagellata. 



512. The Flagellata are widely distributed and there is extreme diversity 

 of form and habit so that the group is difficult to characterize and classify. 

 Many contain chlorophyll and are holophytic, some contain chlorophyll 

 but also ingest particles of food. Some are holozoic, some saprozoic and 

 many parasitic. Special examples of the latter are described in Part III. 

 Those forms which ingest solid food may do so either through a definite 

 oral]opening or the food may be engulfed at the surface where no preformed 

 mouth occurs. In one group, the Choanoflagellata, the base of the single 

 flagellum is surrounded by a collar-like membrane. The flagellum jerks 

 the food particles against the outside of the collar and from there they pass 

 into the cell-body. Undigested fragments of food substances are ejected 

 at the base of the flagellum, within the collar. Some of the Flagellates 

 form swimming colonies by the adhesion of a group of cells to each other. 

 Others are stalked and adhere in groups to form fixed colonies The 

 Dinoflagellata are highly specialized fresh-water or marine Mastigophora. 

 The cell has two flagella, usually placed at right angles to each other, and 

 hidden in deep grooves on the surface of the cell wall. The cell often has 

 a very odd form and is covered with cellulose plates which are fancifully 

 ornamented. Many species contain chromatophores of yellowish, brown- 

 ish or greenish color. The Cystoflagellata are another small group of 



