172 PROTOZOOLOGY 



with starch-formation. Reserve food substances are starch, oil, 

 etc. (p. 94-95). 



In less complicated forms, the body is naked except for a 

 slight cortical differentiation of the ectoplasm to delimit the 

 body surface and is capable of forming pseudo])odia. In others, 

 there occurs a thin plastic pellicle produced by the cytoplasm, 

 which covers the body surface closely. In still others, the body 

 form is constant, being encased in a shell, test, or lorica, which is 

 composed of chitin, pseudochitin, or cellulose. Not infrequently a 

 gelatinous secretion envelops the body. In three families of 

 Protomonadina there is a collar-like structure located at the 

 anterior end, through which the flagellum protrudes. 



The great majority of Mastigophora possess a single nucleus, 

 and only a few are multinucleated. The nucleus is vesicular and 

 contains a conspicuous endosome. Contractile vacuoles are always 

 present in the forms inhabiting fresh water. In simple forms, the 

 contents of the vacuoles are discharged directly through the body 

 surface to the exterior; in others there are several contractile 

 vacuoles arranged around a reservoir which opens to the exterior 

 through the so-called cytopharynx. In the Dinoflagellata, there 

 are apparently no contractile vacuoles, but non-contractile 

 pusules (p. 217) occur in some forms. In chromatophore-bearing 

 forms, there occurs usually a stigma which is located near the 

 base of the flagellum and seems to be the center of phototactic 

 activity of the organism which possesses it (p. 79). 



Asexual reproduction is, as a rule, by longitudinal fission, but 

 in some forms multiple fission also takes place under certain 

 circumstances, and in others budding may take place. Colony- 

 formation (p. 140), due to incomplete separation of daughter in- 

 dividuals, is widely found among this group. Sexual reproduction 

 has been reported in a number of species. 



The Mastigophora are free-living or parasitic. The free-living 

 forms are found in fresh and salt waters of every description; 

 many are free-swimming, others creep over the surface of sub- 

 merged objects, and still others are sessile. Together with algae, 

 the Mastigophora compose a major portion of plankton hfe 

 which makes the foundation for the existence of all higher aquatic 

 organisms. The parasitic forms are ecto- or endo-parasitic, and 

 the latter inhabit either the digestive tract or the circulatory 

 system of the host animal. Trypanosoma, a representative genus 



