POWEE OF SUCTION IN CRIBRINA 221 



attached to a Cribrina, they are found to be securely held in 

 place. Yet if the animal is transferred to a laboratory tank 

 and especially to a vessel of standing water, many of these frag- 

 ments soon drop off. Gee ('13, p. 307) has observed that the 

 injection of a solution of potassium chloride or of beef juice into 

 a fresh Cribrina in a tide pool causes many of the fragments to 

 be shed at once. A denuded Cribrina put into a rocky crevice 

 soon covers itself again with fragments of shell and gravel. 

 Apparently the tubercles act as suction organs and quickly take 

 hold of fragments of shell or drop them in accordance with 

 circumstances. 



If a Cribrina is placed on its side in an aquarium, it soon 

 attaches itself by the suction of those tubercles that are next 

 the bottom of the aquarium and near the pedal disc. It then 

 gradually turns itself on to its pedal disc and eventually the 

 attached tubercles drop their hold. Thus the suction of the 

 tubercles is an essential element in the righting reaction of this 

 sea-anemone. 



As it is possible to find fragments of shell of considerable size 

 attached to the sea-anemone by only a single tubercle, it is not 

 difficult to arrange apparatus to measure the force necessary to 

 break the attachment, for when the shell is drawn away from the 

 sea-anemone, it and the tubercle always separate on their natural 

 surfaces. 



To accomplish such measurements, a spring balance was 

 adjusted overhead so that a string could be brought from it 

 vertically downward into an open glass vessel in which was a 

 Cribrina. The string was now tied to an appropriate fragment 

 of shell and the vessel lowered till the shell and tubercle sepa- 

 rated. The force just necessary to accomplish this separation 

 was indicated on the scale of the spring balance and recorded. 

 The area of the attachment of the tubercle to the shell was 

 usually clearly marked on the shell and this was also measured 

 and recorded. Such measurements were facilitated by choosing 

 tubercles that had become attached to the flat face of a bit of 

 shell and whose area of adhesion was bounded by an approxi- 

 mate circle, a not unusual form of attachment. The records 

 from ten trials are given in table 1 . 



