244 H - p - KJERSKOG AGERSBORG. 



Migratory Movements. 



Statements have already been made to the point that Pycno- 

 podia possesses locomotive powers great enough so as not to be 

 caught by the outgoing tide, provided that the land is not too 

 flat. The rate of tidal recession, even during times of extreme 

 low-tide, will not be faster on a slope of six inches to the distance 

 of twelve and a half feet, than Pycnopodia is able to keep pace 

 with. In addition to these kinds of movements which have been 

 mentioned, Pycnopodia seems to move according to seasons of the 

 year. Seasonal movements, as they may be called, have three 

 underlying primary causes, to wit: reaction toward light, search 

 for food, and the breeding impulse. These three are causes for 

 extensive migrations. 



Reaction toward Light. During the summer time Pycnopodia 

 is found, as a rule, in deeper waters. If found in shallow water 

 during this time of the year it will almost always be in shaded 

 places, as under docks, under kelp, algae or on the shaded side of a 

 bay. This seems to point to negative heliotropism. In the spring, 

 1915, during the breeding season, Pycnopodia was found actually 

 congregated in large numbers on the sunny side of the bay, but 

 two months later there was not a single specimen on that side 

 of the bay, while on the shaded side of the same bay a few were 

 found under a dock, but farther out than during the spring and 

 winter. Movements of this nature vary, however. As was 

 seen during the summer of 1916, when the whole summer was 

 exceptionally rainy, cloudy and cool, Pycnopodia seemed to take 

 advantage of such conditions and remained in shallow water all 

 the time. August, however, proved to be more sunny and warm 

 than the early part of the summer, with the effect that the rays 

 of the sun became annoying to the star. This unexpected and 

 intense light caused every single specimen, as far as could be 

 observed, to move away, either down to deeper water or to 

 hide under some object. The dock, as an illustration (Fig. 3, 

 Minette side of the bay, starfish area ACBD), served as a satis- 

 factory shading place, where Pycnopodia actually congregated in 

 a continuous layer from three feet depth to as far as could be 

 seen at low -water. The question arises: How did the star find 

 the dock to hide under when the sunny days of August suddenly 

 came? 



