INTRODUCTION 



The dinoflagellatcs form an exceedingly important part of the ocean mead- 

 ows, the source of the primitiA'e food supply of the sea, both in the number of 

 individuals and in the total mass of living substances produced. They abound 

 both in neritic waters and in the high seas and range from the tropics to the 

 polar oceans. As SATithetie producers of carbohydrates, proteins, and fats they 

 hold high rank among the protists of the sea and of fresh water. In abundance 

 they are second only to the diatoms in the marine plankton, while locally and 

 in midsummer they may far outnumber even these abundant organisms. At 

 their periodic maxima they may surpass the diatoms in the total mass of sub- 

 stance producd and in the rapidity of their development. These local massive 

 developments are the primary and all but universal cause of the discolored seas, 

 and of the phenomenon of the "Mare Sporco," or luminescent w\aters, which 

 are wont to occur in midsummer in neritic regions and on the high seas, espe- 

 cially in the tropics and along the western shores of the American continents. 

 Similar extensive growths of fresh-water dinoflagellates, especially of Ceratium, 

 cause reddish discolorations in reservoirs and lakes in midsummer. 



The phenomenon of the phosphorescence of the sea has been known since 

 Pliny (see Bostock and Riley, 1885) noted the fact that "there are sudden fires 

 in waters." But the organisms which are responsible for the most of the light 

 in the ship's wake and in the breakers along shore have been studied but little, 

 and the light they shed is often erroneously attributed to the Copepoda or 

 exclusively to Noctiluca, while in reality it may often be due to other dino- 

 flagellates. 



No monograph on the Dinoflngellata is included in the reijorts of the Chal- 

 lenger Expedition, and P/jrocijstis, the most brilliant dinoflagellate of the high 

 seas, was described by Sir John Murray as a diatom. Even our most widely 

 knoAvn Texthook of Zoology (Parker and Haswell) erroneously ascribes to the 

 neritic genus Noctiluca the phosphorescence of the high seas. 



The purpose of this monograph is to set forth a summary of our present 

 knowledge of the most elusive and least known representatives of the dinofla- 

 gellates, namely, the naked or unarmored forms. Many of these are most 

 brilliantly colored, vjdng with the orchids and ])utterflies in A-ariety of color 

 and delicacy of shading, although microscopic in size. They also include some 

 of the most highly organized and uniquely specialized of the greatly diversified 

 group of Protozoa, presenting species possessing, among other organs, a struc- 

 turally complicated ej^e with lens, pigment mass, and sensory core, also a mobile 

 tentacle-like structure, and nematocysts not less specialized than those of the 

 coelenterates. These highly specialized species exist moreover within a group 

 of protists in which holozoic and lioIoi)hytic nutrition occur in different species 

 within the same genus. The great fimdamental function of nutrition has not 



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