2 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



in the dinoflagellates reached that definite degree of differentiation which de- 

 limits the animal and vegetable kingdoms. On this basis liotanists and zoologists 

 alike will contim;e to regard the dinoflagellates as within the legitimate scope 

 of their several fields. The present paper increases the evidence for a much 

 greater representation of holozoic forms among the dinoflagellates than has been 

 hitherto known. ISIuch confusion has accordingly arisen in the study of Dino- 

 flagellata due to the fact that the group contains both holozoic and holoph}i:ic 

 organisms, with the result that the literature dealing with them has been divided 

 between the botanical and zoological fields, with a consequent lack of correlation. 



Furthermore, the organisms themselves, as shown aljove, are usually ex- 

 ceedingly sensitive to adverse conditions on removal from their normal habitat, 

 do not long survive microscopical examination, and are subject to progressive 

 changes as dissolution approaches. As a result these pathological conditions 

 have sometimes appeared in the figures and descriptions as normal phases of 

 form and function. This is especially true of the delicate, pelagic represent- 

 atives of this group. It is hoped that the present paper will be of use in clearing 

 up some of the obscurities which still remain regarding a nmnber of species of 

 the group. 



This monograph also sets forth the authors' conceptions of the relationships 

 of the genera within the group, which differ materially in a number of partic- 

 ulars from those of previous investigators in this field. One feature of some 

 significance is the re-alignments necessitated by the discovery that Pyrocijstis, 

 at least as originally described by Mui-ray (1876), is only a phase in the life 

 history of other Dinoflagellata, e.g., Goiiyaidax. A second feature is the sep- 

 aration of Noctilnca from the Cystoflagellata Haeckel (1873) and its inclusion 

 in the ISToctiluciidae, merely a family of the order Diniferidea. The gap which 

 has long separated these from the Dinoflagellata has been so completely bridged 

 liy discoveries, some of them long overlooked, such, for example, as the signifi- 

 cance of Hertwig's (1876) Erythroims, that the isolation of NoctUuca and 

 related forms in a separate order, or even suborder (Jollos, 1910), is no longer 

 defensible. 



The reasons for the slow development of our knowledge of this remarkable 

 group of organisms are their eupelagic habitat and the correlated fact that 

 they are but poorly represented in the neritic plankton. Few marine biolog- 

 ical stations are so located that they have quick and ready access to the pelagic 

 life of the open sea, and the fresh-water species of the G}^nnodinioidae are 

 relatively few and show little differentiation. An additional reason lies in the 

 fact that their period of maxinnun occurrence is in niidsmnmer and that the 

 area of greatest abundance is in the warm temperate and, presumably, the 

 tropical seas. The main reason, however, is to be found in the exceedingly 

 delicate and sensitive nature of the organisms themselves. The turmoil of the 

 filtering water in the plankton net, the crowded state of the plankton collection, 

 and even the conditions of aeration on the microscopic slide are all hazardous 

 in the extreme to the soft and flexible bodies of these dinoflagellates. ^lutilated 



