DIURNAL MIGRATION OF PLANKTON 



25 



ment an individual is either red-dancing or blue-dancing. If the proportion 

 of energy in the short wave lengths is too high, all the animals will blue- 

 dance all the time. Within a range of proportions specific for each species, 

 and probably afifected by several environmental factors such as presence 

 of food or hunger, the individuals will change spontaneously back and 

 forth from one dance to the other. The total proportion of time spent 

 doing each of the dances is extremely sensitive to the proportional energies 

 of short and long wave lengths. A convincing test of this hypothesis may 

 be performed by placing, over a dish of daphnids, a shallow Incite tray 

 having two or more compartments, one of which is filled with clear water 

 and the other with a phytoplankton suspension. If the dish and overlying 

 tray of water and phytoplankton is illuminated from above, the organisms 

 rapidly gather under the phytoplankton. 



Color dances have been observed in several freshwater Cladocera — 

 Daphnia magna, Ccriodaphnia, Moina, and Bosmiita — and also in a fairy 

 shrimp, Eubranchipiis. We have observed color dances in the following 

 marine zooplankters : Squilla larvae, two pontellid copepods, and a har- 

 pactacoid copepod. 



Fig. 2. Statistical behavior associated with food. 

 Arrows indicate relationships. 



