BILATERAL TENDENCIES IN PYCNOPODIA HELIENTHOIDES. 245 



The dock, as seen in Fig. 3, is located near the point of 

 the Minette side of Washington Channel, opposite the City of 

 Bremerton. On no occasion has the writer observed Pycnopodia 

 on the outside of the dock or in the area QPXY, but always on 

 the inner side, toward the Washington Channel. The sudden 

 continuous sunshine which came in August with the temperature 

 the highest in the year soon made itself felt to the negative 

 heliotropic star. Observation on the direction of the rays of 

 light during the middle of the day explains this phenomenon. 

 The light rays of the late forenoon and early afternoon are up the 

 channel, or diagonally from the dock toward the starfish field, 

 ACBD. The cause for the movements and orientation of the 

 star in this particular case must be sought in the phenomenon of 

 the effect of the direction of the most intense rays of light. 



Loeb (6), working on Spirographis spallanzanii, found that 

 rays of light, if sufficiently intense, are unequivocally able to 

 determine the orientation. In summarizing the causes for mov- 

 ing to or from the source of light, he says: 'The direction of the 

 median plane of an animal coincides with the direction of the 

 rays of light. Light of a constant intensity acts as a constant 

 stimulus, in animals as well as in plants." These statements 

 seem to explain why Pycnopodia "found" the dock. The star, 

 however, moved toward the source of light, and according to 

 Loeb's conception of the behavior of heliotropic animals, that 

 should make Pycnopodia positively heliotropic, for, "Positively 

 heliotropic animals will move toward the source of light, even if 

 in so doing they go from places of greater intensity of light to 

 places of less intensity." When the star, however, came under 

 a good shading object, such as the dock offered, it remained there 

 for several weeks, and did not venture away from the dock in 

 either direction. 



As was said above, Pycnopodia occurs in shallow water during 

 the spring and late winter, and in deep water during the lightest 

 part of the year. The early part of summer and late part of 

 winter are the regular migratory periods. The causes for migra- 

 tory impulses have been designated as three: the effect of the 

 rays of light, search for food and the breeding impulse. But in 

 a rather large number of cases movements of Pycnopodia at the 



