28 INVERTEBRATE PHYSIOLOGY 



However, the series of behavior patterns concerned with vertical migra- 

 tion described below can be shown to be associated wdth the presence of 

 the nauplius eye in Daphnia magna. Destruction of the nauplius eye by 

 microsurgery or by needle beam x-rays results in complete disruption of 

 the behavior pattern. Tests have been carried out in the case of each be- 

 havior pattern described for Daphnia magna. Only those behavior patterns 

 associated with vertical migration are disrupted. 



Ultraviolet and violet light produce positive geotaxis and a negative 

 phototaxis which is mediated by the nauplius eye. For example, if a popu- 

 lation of daphnids is suddenly exposed to a horizontal beam of violet light, 

 there results an immediate movement of the population down and away 

 from the light beam. The proportions of the down and away vectors of the 

 locomotion depend on the w^ave length of the horizontal light beam, its 

 intensity, and the state of accommodation of the daphnid population to the 

 intensity of the beam. The down vector is greater the shorter the wave 

 length and is roughly proportional to the intensity. A cinematographic 

 analysis of this stimulus-response situation is being carried out. We may 

 summarize this behavior as follows : 



( 1 ) Dimming wave lengths either shorter or longer than 5,000 A can 

 provoke upswimming. 



(2) Brightening wave lengths shorter than 5,000 A can provoke down- 

 swimming. 



(3) Brightening wave lengths longer than 5,000 A cannot provoke 

 downswimming but may cause a slow spread downward. 



(4) Shifting the spectrum of light toward blue without changing the 

 intensity can provoke downswimming. 



(5) Shifting the spectrum of light toward red without a change in in- 

 tensity can provoke upswimming. 



Fairy shrimp show behavior similar to that indicated for daphnids. 



Light and Vertical Migration 



The vertical response to light stimuli of the inshore plankters of the 

 Inland Waterway of Florida^ is considerably different from that of the 

 freshwater plankters. An increase of light intensity may induce down- 

 swimming and a decrease in intensity may induce upswimming but the 

 intensity changes required are very much greater. A 95% decrease in in- 

 tensity (compared to 1-10% for freshwater Cladocera) is required to elicit 

 a clear, though usually temporary response. Most species having a hori- 



1 The marine work reported here was performed at the Marineland Laboratory, 

 Marineland, Fla. 



