* S CHAPTER IV 



THE MASTIGOPHORA 



THE Mastigophora are provided with a motile apparatus in the 

 form of flagella, which may vary in number from one to many. 

 In the majority of cases, the body is of well-defined and constant 

 form, and covered with a cuticle, menibrane, or shell. They abound 

 in infusions, in stagnant pools, in clear water, and in the sea, while 

 many of them are found as parasites in higher animals, where they 

 live in the cavities and cells of the body. 



In this class are found many diverse types of unicellular organisms, 

 including, at one extreme, primitive forms whose allies are undoubt- 

 edly among the bacteria and the lowest plants (monads), at the other 

 extreme, colonial forms, which in the complexity of their structure and 

 functions are little lower than some of the Metazoa and Metaphyta. 

 It includes forms whose bodies are naked ; others that are clothed 

 with complex membranes, or incased in chitinous, silicious, or cellu- 

 lose shells. It includes organisms with very different methods of 

 food-taking : in some forms the food, like that of the green plants, 

 consists of products made from simple compounds by the organism 

 itself ; in others, the food, like that of the fungi, consists of dissolved 

 organic matters ; and in still others, the food, as in the higher animals, 

 consists of solid particles of proteid and other matters. 



Notwithstanding these many structural and functional differences, 

 there are some well-defined structural characteristics according to 

 which the Mastigophora may be subdivided into a number of more 

 or less homogeneous groups. These groups are the Flagellidia, 

 Dinoflagellidia, and Cystoflagellidia. The first comprises the least 

 homogeneous forms ; they consist usually of minute cells with a 

 simple naked body, which may become more or less amoeboid, and 

 with one, two, or several flagella. In some cases, there is a compli- 

 cated cell-membrane, in others a shell, while colony-formation is fre- 

 quently seen. The Dinoflagellidia are distinguished by the presence 

 of one or two furrows, in which the flagella find their origin, one to 

 pass around the organism transversely, the other to vibrate freely in 

 the surrounding water. The majority are covered by a cellulose 

 shell, consisting frequently of several plates. The Cystoflagellidia, a 

 group consisting of only two genera, Noctiluca and Leptodiscus, are 



