THE MASTIGOPHORA 125 



inclosed by a definite membrane (euglenoids and the majority of 

 Mastigophora ; cf. Figs. 14, C, D, E, and 10, B). Again, it may be in 

 the form of a homogeneous mass in which no granular structure can 

 be seen (many Phytoflagellida), or, as in many Rhizopoda, it may be 

 massed in several such aggregates {Noctihica). Still another arrange- 

 ment is seen in the Dinoflagellidia, where the chromatin is arranged 

 in the form of a twisted thread or threads. Finally, in some forms 

 the resting nucleus closely resembles that of the Metazoa in having a 

 linin network in which the chromatin granules are suspended. 



An integral part of the nucleus is the so-called "nucleolus," which, 

 however, is not analogous to the nucleolus of the Metazoa, but 

 functions as a sphere or the division centre during mitosis. 1 



Nuclear division in all forms of Mastigophora may be regarded as 

 more or less simplified mitosis, or indirect division. In the simplest 

 types the chromatin masses merely draw out and divide into equal 

 parts, but in the more complicated types, the process closely resembles 

 that in the Metazoa, the complete mitotic figure consisting, as in the 

 higher forms, of chromosomes, mantle-fibres, centrosomes, and spheres 

 (Fig. 70). 



D. Food-taking 



Closely dependent upon the mode of living is the manner of taking 

 food. Some forms, which live in foul water, are saprophytic like the 

 colorless plants, and absorb, through the body walls, the substances 

 which are dissolved out of decaying vegetable matter. Those which 

 live in pure and clear water generally have chromatophores, colored 

 by chlorophyl, diatomin, or some allied substances, and have the 

 power of manufacturing their food from carbon dioxide, water, and 

 salts; like the green plants, their nutrition is holophytic. Parasitic 

 forms live upon the juices of other living organisms, which are 

 absorbed through any part of the body wall (Fig. 71). Finally, some 

 take in solid food, which is acted upon and digested by the fluids 

 of their inner plasm, the indigestible portions being excreted as in 

 the higher animals. 



In the holophytic forms there is frequently an unbroken shell about 

 the animal which makes it impossible for solid food to enter {Hcemato- 

 coccus ; many Dinoflagellidia). Many of the holozoic forms have a 

 distinct mouth and oesophagus. In its simplest form the mouth is 

 merely a softened area about the base of the flagellum, against which 

 the solid food particles strike (Oikomonas, see Fig. 18, B). Others 

 have a distinct mouth-opening leading into a gullet, which in turn opens 

 into the fluid endoplasm (Peranema ; Petalomonas, see Fig. 1, B). 



1 See infra, p. 258. 



