390 MORRIS M. WELLS 



in contact were frequently detached with the limpet and re- 

 mained attached to its foot. In many instances, the limpets 

 were attached to the barnacle covered rocks in such a way that 

 one could actually see daylight between the rather loosely set 

 barnacle shells under the animal's foot. Even in these cases, 

 the pull required to detach the limpet was very little if any 

 less, than that required for the other situations and usually the 

 limpet did not leave the rock, without bringing the barnacle 

 cases with it. On the other hand, limpets pulled from glass 

 plates came off with the application of about one-half the force 

 necessary to detach them from the rocks. Calculations, based 

 upon the clinging power of the limpets, indicate that the large 

 Abalones (another gastropod mollusc much larger than the 

 limpets) that are numerous along the coast of southern Cali- 

 fornia can cling with a power equal to 1100 pounds weight. 

 One who has attempted to pull them from the rocks may well 

 credit them with this great adhesive power. 



4. Reaction of limpets to environmental factors. — A large num- 

 ber of readings was taken as to the position which the limpets 

 assume on the rocks, in relation to the current made by the 

 waves, to the pull of gravity, and to the direction of the sun's 

 rays. The readings were taken daily for three weeks. The 

 following table summarizes the results. 



Reaction to — Positive Negative Indifferent 



Current 450-51% 321-36% 117-13% 



Gravity 334-54% 203-33% 73-13% 



Light 285-37% 266-36% 199-27% 



The figures indicate a strong positive reaction to current and 

 gravity but none to the light. It is readily noted that limpets 

 do not occupy the sunny sides of rocks but this is probably a 

 negative reaction to temperature rather than to light. Experi- 

 ments with light gradients will probably indicate a selection 

 of a medium light upon the part of these limpets. In the above 

 experiments the reaction was to direction of rays rather than to 

 intensity since the orientation of the animals, i.e., whether fa- 

 cing toward or away from the sun, were the only data recorded. 



5. The homing instinct. — Observations, continuing in some 

 cases for a little over a month, were carried on, to determine 

 the daily relation of the different species of limpets to a given 

 resting place on the rocks. The idea was, first, to determine 

 whether or not any or all of the species possessed a definite 



