222 



G. H. PARKER 



TABLE 1 



Breaking forces (grams), diameters of suction areas (millimeters), calculated areas 

 of suction (square millimeters) and calculated suction-pressure (grams per sq. 

 millimeter) for ten trials in separating fragments of shell from the suction 

 tubercles of Cribrina. 



Breaking forces in 

 grams 



Diameters of suction 

 areas in millimeters.. . 



Calculated areas of 

 suction in sq. milli- 

 meters 



Calculated suction- 

 pressure in grams 

 per sq. millimeters. . . 



47 

 2.6 



5.3 



8.6 



28 

 1.6 



2.0 



13.9 



29 

 1.5 



1.8 



16.5 



50 

 2.6 



5.3 



9.4 



53 

 2.5 



4.9 



10.8 



38 

 1.8 



2.5 



15.0 



2.9 



6.6 



7.9 



50 



2.6 



5.3 

 9.4 



65 

 3.0 



7.1 



9.2 



60 

 2.9 



6.6 



9.1 



47.2 

 2.40 



4.74 



11.0 



It will be noted from the table that large breaking forces are 

 usually associated with large suction areas, small ones with small 

 areas. The average breaking force for the ten trials is 47.2 

 grams and the average suction-pressure 11 grams per square mil- 

 limeter. This amounts approximately to 15.6 pounds per square 

 inch. As the limit of suction under ordinary circumstances is 

 one atmosphere or 14.7 pounds per square inch, it appears that 

 at the moment of breaking the sea-anemone was exerting probably 

 as much suction as, under the circumstances, was physically 

 possible. 



Although the mechanism of the suction apparatus in Cribrina 

 has not been worked out, it is without much doubt dependent 

 upon muscle, and muscle is said (Howell, '13, p. 41) to vary in 

 the pull it can exert from 7 (up to 30) grams per square milli- 

 meter, in the frog, to 62.4 grams per square millimeter, in man. 

 Hence it may be concluded that, though the suction apparatus 

 in Cribrina has reached a physical limit, it has not necessary 

 reached an organic limit. 



LITERATURE CITED 



Gee, W. 1913 Modifiability in the behavior of the California shore anemone 

 Cribrina xanthogrammica Brandt. Jour. Anim. Behav., vol. 3, pp. 

 306-328. 



Howell, W. H. 1913 A Text-book of Physiology. Philadelphia and London, 

 8vo, 1020 pp. 



