Xo. 5.] THE HABITS OT P \ 'CXOC.OXI 1*S. 203 



at one end of the Pycnogonid as it rests upon the sand. The 

 arrow indicates the direction of the light. The animal at once 

 begins to kick and the body is raised from the bottom, but 

 since those legs on the side from the light (a} beat stronger 

 than those towards the light (b), that side is raised more and 

 the body is tilted so that the rays of light strike approximately 

 perpendicular to the dorsal surface, as shown in B. Since the 

 regular movement of the legs tends to propel the animal dorsal- 

 ward, it moves toward the light. And now the fact that the 

 anterior legs beat more effi- / 



ciently than the posterior must 

 be taken into account ; this 

 action tends to bring these legs A 

 uppermost, that is, around to 

 the place of the legs (a] in 

 diagram B. This is shown in 

 C, where we see the animal 

 from the side instead of end- B 

 wise, as in A and B\ in this 

 position the posterior legs kick 

 along on bottom. As a matter 

 of fact the anterior legs seldom 

 come entirely around so as to C 



be directly Uppermost, but Only FlG . 3 . _ Diagram representing the reaction 



approximate that position, the of Anopiodactyius to light, 



third and fourth legs of one side or the other being the ones 

 to touch bottom rather than the posterior legs ; so that the 

 animal does not move directly backwards but rather "corner- 

 wise." If the movement is more vigorous, or if the light 

 comes more from above, the animal may raise itself entirely 

 free from the bottom, keeping, however, the same relative 

 position. 



If the orientation is different from the case given, it is easy 

 to see how the same result is brought about. In a case where 

 the animal is headed directly from the light, the anterior end 

 has but to raise from the bottom to bring it into this position ; 

 and in the other possible case, when the head is directed 

 towards the light, although the movements may be indefinite 



