134 A STUDY OF WELK 



tidal conditions to meet with new and severe dangers and inas- 

 much as its phylogenetic history has not included exposure to 

 such dangers, the species, responding with a set of reactions 

 that are definitely deleterious and even fatal, perishes helplessly 

 within a meter or two of conditions that would serve to shelter 

 it until the tide again returns and the danger passes. 



During other than the spring phases of tide Buccinum 

 iindatum, being a gastropod of more than ordinary motor acti- 

 vity becomes dispersed more and more in the shoreward direc- 

 tion together with such forms as the sea urchin, Strongylocen- 

 trotus drobachiensis and the starfish, Aslerias -vulgaris. When 

 the tides pass into the spring phase and the amplitude of tidal 

 change rapidly increases these shcrevvard migrants are suddenly 

 thrust from conditions of continuous immersion in sea water at a 

 temperature of eight degrees centigrade to conditions of daily 

 exposure for hours to the summer sun. 



To study the normal activity of Buccinum in this situation 

 four series of animals aggregating 152 individuals were marked 

 and released some at low tide level immediately following a 

 spring tide, others at the upper limit of intertidal zone reached 

 by Buccinum immediately after a spring tide. The methods of 

 marking used were such that, as controls amply demonstrated, 

 the animals were in every way physiologically normal. Sub- 

 sequent careful searches were made for and records kept of 

 these individuals. The results may be briefly summarized as 

 follows. The released animals wandered in all directions there 

 being no evidence of any shoreward or seaward directive in- 

 fluence. The rate of what may be termed "walking dispersal" 

 varied greatly for individuals some of which remained near 

 where they were liberated for as long as five weeks. There 

 was an entire absence of any protective migration toward nearby 

 areas off^ering optimal conditions of shelter. The most signifi- 

 cant and unexpected result however occurred in the instance of 

 the animals set free during spring tides at the upper level reached 

 by Buccinum. Forty-eight hours later eighteen of the animals 



