38 MANUAL OF ZOOLOGY sect. 



multiple fission takes place, and flagellul<z, i.e., young pro- 

 vided with flagella, are produced, which, sometimes after 

 passing through an amoeboid stage, develop into the adult 

 form. 



In the other Mastigophora the body may have a shape 

 similar to that of Euglena, or may be longer and narrower, 

 or, on the other hand, may be short and thick, ovoid or 

 globular. Anterior and posterior ends are nearly always 

 distinguishable, the former being that which is directed 

 forwards in progression. Usually there are distinct dorsal 

 and ventral surfaces, the former being that which is habitually 

 directed upwards. In most cases the body is equal-sided 

 or bilaterally symmetrical, i.e., is capable of being divided 

 into two equal lateral portions along the median vertical 

 plane ; but sometimes it is unsymmetrical, one side differ- 

 ing more or less from the other. In most the body is, as 

 in Euglena, naked ; but some have a chitinoid shell or lorica, 

 while others have a firm cell-wall of cellulose which may 

 present an elaborate pattern of strips, dots, etc., and may be 

 produced into long processes. Most of the Mastigophora 

 are, like Euglena, free-swimming, but some are permanently 

 attached by means of a slender stalk (Fig. 13, 10, ij, 14; 

 Fig. 14, 1, j). 



The number and arrangement of the flagella vary greatly. 

 The number may be one, as in Euglena, or two, three, or four. 

 In forms with two flagella these are both attached at or near 

 the anterior end, and often take on different functions, one 

 of them, directed forwards, being alona- used in locomotion, 

 while the other is trailed behind when the animal is swim- 

 ming freely, or is used to anchor it to various solid bodies. 

 In one large group of Mastigophora, the Choanoflagellata 

 (Fig. 14), there is, surrounding the base of the flagellum, a 

 remarkable vase-like prolongation of the protoplasm, ex- 



