KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 3 



individuals of such delicate siDecies as Gifmnodinium rubrum were almost as 

 abundant in our plankton eollections as were normal ones. 



These species are also noticeably sensitive to illumination and imder condi- 

 tions of microscopical examination undergo e^'tolvsis rather quickly. Some 

 of the more delicate ones succumb in a few moments after exposure to the 

 intense illumination of the high-power microscope. Others survive for a longer 

 time, though rarely for as much as an hour, while in every ease the organisms 

 begin to round up, lose very quickly their characteristic contour, distinctness 

 of sulcus and girdle, and normal color and distribution of pigment or other 

 colored substances, in the confinement of the microscope slide. The result is 

 that as soon as the organisms quiet down sufficiently to permit observation and 

 analysis of structure they begin to give more or less distorted pictures of their 

 real organization. The rounding i;p and increasing vacuolation which attend 

 the initial phases of cytolysis are evident in many published figures of species 

 in the group, including some in this paper. 



Other reasons for the lack of observations on the G}Tiinodinioidae are the 

 ra]>idity of locomotion and incessant movements of many of the species, espe- 

 cially of the smaller forms. The larger ones, such as Noctiluca, readily permit 

 observation since flagellar activity is slight with reference to the total mass of 

 the organism, and both rotation and locomotion are relatively feeble in this 

 and other large forms. On the other hand, there are a host of minute forms 

 which have thus far eluded pursuit, or, if pursued by the aid of the mechanical 

 stage, they never sta.y quiet long enough at a time to permit observation, much 

 less an accurate drawing. AVe have not found it possible to make use of any 

 anaesthetic or taxing agent to Ijring these active forms under observation. The 

 few more resistant species, such as Polykrikos schwartzi and Gymnoclinium 

 lint, which survive the diffusion currents resulting from the admixtures of sea 

 ^^■ater and the chemic^als i;sed in fixation, are more or less contracted and dis- 

 torted, wliile the majority of species are wholly disrupted or mutilated and 

 contracted beyond recognition by attempts at fixation for cytological study. 

 The cytoplasm of these organisms is so nearly labile that the use of any of the 

 kno'wn cytological and protozoological methods has thus far failed to preserve 

 their structure satisfactoi'ily for subsequent staining, mounting, and permanent 

 preservation of specimens. There are therefore few if any type specimens in 

 existence of species in this group. 



The investigator of the group is thus limited to the primitive and sim})le 

 method of observation of the living organism in action. This has its advan- 

 tages, for while we may not determine the finer cytological detail as preserved 

 more or less unperfectly in the coagulated and sectioned substance of the 

 organism, we do haA'c, under such cduditions of examination of these active and 

 mobile dinoflagellates, a near approach to the noi'innl form, and in most cases 

 an exce])tional transparency of the living substance, which makes ])ossi])le an 

 analysis, in the natural state, of internal structure, to a degree of completeness 

 which is rareh' equaled in the investigation of the Protozoa. 



