PLASMODROMA, MASTIGOPHORA, CHRYSOMONADIDA 83 



materials consisting of oil and carbohydrates are occasionally 

 found. 



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

 a slight cortical differentiation of the ectoplasm to delimit 

 the body surface. Such forms are capable of pseudopodial for- 

 mation. In others there occurs a thin expansible pellicle secreted 

 by the ectoplasm, which covers the body surface closely. These 

 forms are often plastic and change their form in a peculiar 

 fashion (Fig. 6). In still others the body is constant, being en- 

 cased in a shell, test, lorica, or plate, which is composed of chitin, 

 pseudochitin, or cellulose. Not infrequently a gelatinous secre- 

 tion envelops the body. In one group, Choanoflagellidae, there 

 is a collar-like structure located at the anterior end surrounding 

 the flagellum. 



The great majority of the Mastigophora possess a single 

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

 usually of vesicular type with a conspicuous endosome. Con- 

 tractile vacuoles are always present in the forms inhabiting 

 fresh water. In the 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 Dinoflagellida, there are apparently no 

 contractile vacuoles, but non-contractile pusules, which seem 

 to have hydrostatic function, are present in the cytoplasm. In 

 forms with chromatophores, there occurs usually a reddish or 

 brownish, rounded or elongated body, the stigma, which is 

 situated near the base of the fiagellum. It seems to be the center 

 of phototropic activity of the organism which possesses it. A 

 number of Mastigophora are capable of forming pseudopodia of 

 various types which serve for food-capturing and locomotion. 



Asexual reproduction of the Mastigophora is, as a rule, by 

 longitudinal fission, but in some forms multiple fission also oc- 

 curs under certain circumstances, and in others budding may 

 take place. Colony-formation, due to incomplete separation of 

 the daughter individuals, is widely found among the group. 

 Sexual reproduction has been noted in a number of species. The 

 development varies among different groups and will be briefly 

 taken up for individual orders. 



