KOFOID AND SWEZY: UNARMORED DINOPLAGELLATA 9 



these delicate organisms to slight environmental changes. These responses are 

 usually shown in the form and dunensions of the body. It is only in compara- 

 tively rare cases that an individual may be kept under observation under the 

 microscope long enough for a complete camera drawing, without these changes 

 in the body manifesting themselves. Often indeed they have begun when the 

 drop of water containing them is first imprisoned by the cover slip (fig. A). 



Fig. A. Variations in size and shape of Gymnodinium rubrum sp. nov. 1. Individual showing the normal 

 appearance of the body. 2-5. Individuals all taken from the same haul and showing variations in size and shape. 

 X 355. 



These changes consist of a gradual but slight increase in diameter and a pro- 

 gressive rounding up of the body, with obliteration of the furrows, ending in 

 complete disruption of the entire organism. The rounding up or thickening 

 of the body, resulting in a diminished length and increased diameter, is a 

 common condition in plankton hauls that have remained in the laljoratory for 

 half an hour or more, particularly if any great length of time has elapsed 

 between the actual taking of the haul and its appearance in the laboratory. 

 In hauls containing an abundance of material this degenerative process is much 

 more rapid than where the change from the more highly oxygenated oceanic 

 waters is not emphasized by overcrowding. 



The same effect may sometimes be produced by the ingestion of large food 

 bodies, that is, the body liecomes shorter and broader to accommodate the food 

 mass (pi. 5, fig. 56). After the process of digestion is completed the body 

 gradually resumes its normal shape and size. 



