262 journal of Comparative Neurology and Psychology. 



alone, is the larval lobster able to execute those movements which 

 determine his progress either toward the source of illumination or 

 away from it ? 



If the larval lobsters in any of the first three stages be put in a 

 glass jar w^hich is surrounded by black paper and placed in sub- 

 dued daylight, the short vibratory strokes of the exopodites can 

 be readily observed. At one time, certain individuals may be 

 seen to swim rapidly backward, and again forward, with no appar- 

 ent change in the position of the body or in the direction of the 

 stroke of the exopodites. If, however, the thoracic appendages 

 themselves be carefully watched, one can observe that, from time 

 to time, these limbs undergo either a forward shifting (extension) 

 as shown in Fig. 8, or a backward shifting (contraction) as shown 

 in Fig. 9. This change from the "anterior" position to the "pos- 



FiG. 8. Fig. 9. 



Fig. 8 shows a larval lobster with the thoracic appendages in the extended or 'anterior" position; 

 the resulting movement is forward and upward. • 



Fig. 9 represents the appendages in the contracted or "posterior" position; the resulting move- 

 ment is backward and upward. 



terior ' position may occur at short intervals, each position may 

 persist for some seconds, or there may be a successive alteration 

 with periods of longer duration in either one position or the other. 

 It may be observed further, that when the thoracic appendages 

 take the "anterior" position, the direction of the strokes of the 

 exopodites becomes somewhat forward as well as downward, and 

 the resulting motion of the larvce becomes backward and upward. 

 When, on the other hand, the thoracic appendages assume the 

 "posterior" position, the stroke of the exopodites becomes back- 

 w^ard and downward; and the resulting motion of the larvce becomes 

 forward and upward. During a great part of the time, the upward 

 movement of the larvae, as a result of the outward and downward 

 stroke of the exopodites, does little more than compensate for the 

 natural tendency to sink toward the bottom. For this reason the 



