Hadley, Behavior of the American Lobster. 205 



ward or forward or upward as the case may be," and allowing it 

 to sink toward the bottom when their motion ceases. The progres- 

 sive movement and the body-orientation of the lobster in the first 

 three stages are almost wholly dependent upon the activity of these 

 organs. Occasionally, darting backward movements, caused by 

 the sudden contraction of the abdomen, appear, but these are of 

 slight importance in the reaction to light. 



When the lobster moults to the fourth stage, thf exopodites are 

 lost. Consequently the forward swimming during and after the 

 fourth stage is dependent upon the action of swimming appendages 

 which after the second stage make their appearance on the under 

 sides of the second, third, fourth and fifth abdominal segments. 

 The fourth-stage lobsters swim with directness and precision, usu- 

 ally near the siirface of the water. This surface-swimming may 

 be due to stimulation by light, but, as the writer has suggested 

 elsewhere (1906b), it is not improbable that this form of behavior 

 is due in part to the food-seeking impulse. During the latter part 

 of the fourth stage, contact-irritability begins to play an important 

 role in determining the behavior of the young lobster. Now, as in 

 the fifth and later stages, the creature no longer swims at the sur- 

 face of the water, but seeks the bottom and attempts to burrow 

 in the sand or beneath any object that presents itself. After the 

 fifth stage, the adolescent lobster shows the same type of behavior 

 as during the fifth stage, but with a gradual increase in the tend- 

 ency to avoid light. Its reactions have now become fixed in every 

 way. 



III. APPARATUS AND METHOD OF PROCEDURE. 



The manipulation of the various pieces of apparatus here de- 

 scribed will be spoken of when the particular experiments in which 

 they are used are mentioned. The room in which the experiments 

 were conducted contained on two of the opposite walls windows 

 2 feet high and 8 feet long, before which extended work benches or 

 tables. The two windows, which opened respectively to the east 

 and west, were the only source of daylight, and, as occasion re- 

 quired, were heavily screened with black paper or cloth. At 

 appropriate places in these screens were cut openings which could 

 be readily closed. On the table before one of the windows was 



- For details on method of swimming, see p. 258. 



