MORPHOLOGY AND TAXONOMY OF MASTIGOPHORA 271 



the more common forms of contractile vacuole; the other, called 

 the sac piisule, is very large and tends to assume the general shape 

 of the cell, opening by a fine canal to the outside. Their functions 

 are problematical but they are generally regarded as serving an 

 hydrostatic finiction. 



In one group of forms, the Phytodinidse, the characteristic struc- 

 tural features, furrows, flagella, etc., are absent, the organisms, like 

 unicellular plants, either floating, lying freely on the bottom or 

 attached to it. The nucleus and chromatophores, however, are of 



1 



Fig. 130. — Gymnodinium lunula (Schiitt). Nuclear dhnsion in large pelagic cysts 

 (1 and 2); 3, so-called "horned" cyst; 4, four products of division of 2; 5, eight 

 Gymnocli?iium-like products of horned cyst. (From Doflein after Dogiel.) 



the dinoflagellate type and Klebs, and later students of the group, 

 have no hesitation in placing them with the Dinoflagellida. This 

 is supported by numerous transitional forms from the t\'pical mem- 

 bers of the order; some of these are similarly quiescent, devoid 

 of flagella, but possess the characteristic furrows; others possess 

 flagella and furrows for a period in the life history but lose them and 

 become quiescent and plant-like. Some types of the latter secrete 

 gelatinous coatings (Glceodinnnn), others form peculiar reproductive 

 cysts "horned cysts" (Fig. 130). These aberrant types of Dino- 

 flagellida illustrate the same phenomenon of motile and quiescent 



