INVBRTEBRATA. 431 



in solution. Only a single nucleus. Reproduction by 

 fission, conjugation occurring regularly at certain stages in 

 the life-history, and resulting in the formation of resting 

 spores surrounded by a firm sporocyst, within which the 

 protoplasm divides into several minute sporozoites. Cilia 

 never present, amoeboid stages may occur, and the micro- 

 gametes are frequently flagellate. 



Monocystis and Coccidium are typical examples of 

 Sporozoa, and represent the two great divisions of the 

 Telosporidia, namely the Gregarinida and the Coccidiidea. 

 The essential difference between the two groups is the 

 association of the gametocytes in Gregarinida in a common 

 cyst ; the Coccidiidea are also more permanently intracel- 

 lular. 



CLASS: FLAGELLATA. 



Protozoa which move by means of long flagella which 

 are either single or few in number ; pseudopodia either 

 absent or transitory; a firm cuticle or cell- wall usually 

 present ; nucleus single, or if multiple not differentiated ; 

 nutrition holozoic, saprophytic, or holophytic ; reproduc- 

 tion by fission, sometimes alternating with conjugation, 

 the zygote breaking within a cyst into minute spores. 



The Class Flagellata is somewhat artificial, since many 

 other Protozoa have flagellate stages, e.g. the microgametes 

 of Coccidium, and many forms are placed in this group 

 which by botanists are regarded as plants, e.g. the Volvo- 

 cidae. The group can scarcely be said to belong exclusively 

 to the animal kingdom or to the vegetable kingdom, as 

 many of its members combine the characters of animals 

 and plants, or show in allied forms a transition from an 

 animal character to a vegetable. In mode of nutrition the 

 same individual may be at one time holozoic, at another 

 saprophytic, or, like Euglena, at one time holophytic, at 

 another saprophytic, according to the conditions of life. 

 Even the presence of cellulose is not diagnostic, for the 

 Dinoflagellates, which are common in the sea, have a 

 cellulose membrane, and yet some of them lose their 

 chromatophores and take in solid particles and digest them 

 like an amoeba ; many of them also possess a contractile 



