240 H. P. KJERSKOG AGERSBORG. 



float. The specimen was fed on small shell-fish of the families 

 Cardiidae and Leptonidse; on gasteropods: Amphissa versicolor 

 and also on crabs (Pugettia gracilis, Cancer orgonensis}. Sub- 

 sequent experimenting with this specimen showed the same gen- 

 eral results. When using mature specimens the same general 

 phenomenon was observed. 



The righting reactions may be represented by curves which 

 may show the whole working of fifty trials of righting. These 

 curves also show the indication of fatigue, and are, therefore, 

 called righting reaction-fatigue curves (Fig. i). The abnormal 

 or confused rightings are omitted from curves, hence the break 

 between the respective curves. The number of trials are plotted 

 on the abscissa. The speed in righting reaction is indicated by 

 squares on the ordinates which in turn stand for minutes. 

 Curve A A equals trials 1-19 (the twentieth trial omitted in 

 figure); curve BB equals trials 22-31; curve CC equals trials 

 33-46; curve DD equals trials 49-50. 



These curves when superimposed show an interesting figure 

 (Fig. 2). There is the same picture as in Fig. I, an indication of 

 fatigue, toward the last. However, curve AA has an average re- 

 action speed of 66 seconds per righting; curve BB has an average 

 reaction speed of 55 seconds per righting; curve CC has an 

 average reaction speed of 52.7 seconds per righting. This shows 

 that the speed per average reaction is increased after each turn 

 toward the posterior end, and that may indeed count for the 

 difference in increase of speed in the turnings toward the anterior 

 end, that is, it becomes easier to turn toward the anterior end 

 after it has tried to right itself in some other direction. 



Tidal Movements. 



Pycnopodia moves rapidly enough so as not to be caught by 

 the outgoing tide. Its success in this regard is partly due to its 

 habit, partly because of its physical need to be submerged, and 

 it has therefore developed a speed of movements great enough 

 to enable it to keep submerged all the time. During high-water 

 it may move a considerable distance above low-water mark, 

 and during such time be found on grounds which will be dry at 

 low-water. In such cases it will move a little ahead of the tide, 



