IN VER TEBRA TE MORPHOL OGY. 



substance in which a large number of nuclei are imbedded, 

 sometimes aggregated into masses each of which is sur- 

 rounded by a delicate membrane. It seems probable that 

 these masses represent a process of spore-formation, but as 

 yet nothing is known regarding the further development of 

 the spores. 



III. CLASS FLAGELLATA. 



The Flagellates are characterized by the possession of 

 one or more long filamentous processes of protoplasm, known 

 &sfl,agella, which, by whip-like movements, propel the organ- 

 isms through the water in which they live, and at the same 

 time by the production of currents in the water bring food- 

 particles within their reach. Some forms possess pseudo- 

 podia in addition to the flagella, which are indeed simply at- 

 tenuated and mobile pseudopodia, but the majority have a 

 more or less permanent body-form. This in many species 

 is accompanied by the formation at the exterior of the body 

 of a skin or cuticle which in some cases, as in the Dino- 

 flagellata, may assume a sufficient density and thickness to 

 entitle it to be termed a shell. 



1. Order Autoflagellata. 



In the Autoflagellata the body is usually more or less 

 oval, and while in many forms it is naked and capable of 

 changing form (Fig. 13, A], yet in others special cuticular in- 

 vestments may be present, taking the form in some cases of 

 a simple cuticular covering, as in Euglena (Fig. 13, 12), in 

 others forming a stalk by which the organism is attached 

 to a foreign body ; in some forms, as in Codosiga (Fig. 13, 6'), 

 a cuticular collar surrounding the base of the flagellum is 

 present, while in others, such as Dinobryon, a cup is formed, 

 within which the organism lives. 



Usually but one or two whip-like flagella are present, 

 though occasionally a larger number (6 or 8) may occur, and 

 in some instances one or more may assume a firmer character 

 and serve for fixation of the organism. All forms possess 

 a single nucleus and a contractile vacuole. In the simpler 



