Is NATHAN FASTEN 



making their way from the dark side of the dish to the lighted 

 region. In two instances, the organisms were timed. In the 

 first case it took the copepods five minutes to traverse the 

 entire length of the dish, while in the second instance the time 

 was six minutes. 



3. Behavior in light of low intensity. — In light of low intensity, 

 the copepod does not react quite as definitely as in strong light. 

 This was brought out by the following experiment. An oblong 

 elass dish was used, whose dimensions were the same as those 

 of the oblong dish used in the previous experiment. Eight 

 copepods were placed into it, and with a 60 c. p. Mazda lamp 

 these were attracted to one end. Then the current was turned 

 on to a 1 c. p. bulb stationed at the opposite end, while at the 

 same time the other globe was extinguished. But the organ- 

 isms paid little attention to the faint glimmer. Two or three 

 of them were observed to travel a very short distance to the 

 light, but no definite orientation occurred. When a 4 c. p. bulb 

 was substituted for the ic. p. lamp, the same behavior resulted, 

 no specific orientation taking place. If, however, an n c. p. 

 globe was switched on, the animals oriented definitely, but 

 slowly. They all moved to the illuminated side of the dish. 

 A 16 c. p. bulb brought about this reaction more readily, and 

 globes of higher intensity increased the positive behavior ac- 

 cordingly. 



From these observations it becomes evident that the definite- 

 ness of orientation of the copepod varies with the intensity of 

 illumination. Any increase in the illumination brings about a 

 corresponding increase in precision of the specific reaction of 

 the animal. Yerkes (1900), has noticed a similar behavior in 

 Daphnia and Cypris. 



The above experiments tend to bear out what was observed 

 concerning the behavior of the copepods in their normal sur- 

 roundings. While conducting hatching experiments it was 

 noticed that whenever the covers of the hatching tanks were 

 removed, the copepods would suddenly bob up to the surface 

 of the water from underneath. This was observed many times 

 and the regularity of its occurrence was very striking. The only 

 explanation that could be found for this behavior was that the 

 increase of illumination within the tanks attracted the animals 

 to the surface. With this in mind, the foregoing series of light 



