THE BEHAVIOR OF A PARASITIC COPEPOD 45 



tact with the necessary host, attachment immediately takes 

 place, and the life of the individual and its progeny is secure. 

 If, however, the organism does not meet the host, it tries other 

 regions. The copepod perishes if its movements do not meet 

 success within a given time. 



V. REACTIONS TO CONTACT 



Lernaeopoda is often found adhering to small bits of alga and 

 other substances that float about loosely in the water. A glass 

 rod or a needle may be slowly brought in contact with the body 

 of the copepod, without producing the avoiding reaction. The 

 organism may even adhere to the object for some period. When 

 an object rapidly approaches the animal, it immediately shifts 

 its position, thus avoiding the obstacle. Tapping or jarring a 

 dish containing the copepod, even blowing on the surface of the 

 water, or allowing a drop of water to fall directly above a rest- 

 ing copepod, calls forth the avoiding response; the animal 

 quickly leaves its initial position and moves to other regions. 

 When a copepod is picked up in a pipette and transferred to 

 another dish of water, it almost always sinks to the bottom and 

 remains motionless for a few seconds. Then it begins to dart 

 about actively. In general, Lernaeopoda reacts positively to 

 contact stimuli which are weak in character, whereas to strong 

 stimuli it is negative. 



VI. REACTION TO GRAVITY 



Normally, Lernaeopoda responds positively to gravity. Its 

 specific gravity is heavier than that of water, and it therefore 

 tends to sink to the bottom. This was determined by the fol- 

 lowing experiment. Six copepods were placed in a test-tube 

 filled with water and this was then tightly corked. When the 

 tube was held in a vertical position, the organisms were ob- 

 served to sink to the bottom, with their bodies almost vertical 

 and their heads downward. As soon as they reached the bot- 

 tom of the tube, the animals assumed a horizontal position, 

 either ventral or dorsal, -and began to move about actively. 

 When the tube was reversed the larvae again sank to the bottom 

 in their characteristic way. When the side of the test-tube was 

 lightly tapped, while the copepods were passively sinking down- 

 ward, they were observed to instantly dart upward again. How- 



