84 TJnivers'ty of California Publications in Zoology. [Vol. 4 



(a) Sometimes there is no response to the first stimulus; 

 but this and one or two succeeding ones cause a gradual change 

 in physiological state, so that the pedicellariae later open. 



(b) Sometimes the first stimulus causes retraction and clos- 

 ing, while later ones of the same kind produce extension and 

 opening. 



(c) Sometimes (in the large pedicellariae) the first stimulus 

 causes slight momentary opening ; the next two or three have no 

 visible effect ; the next, pronounced opening. 



2. Chemical stimuli of a certain character cause the pedi- 

 cellariae to open later more readily under mechanical stimuli. 



S. Chemical stimuli of a certain character cause later refusal 

 to open under the usual mechanical stimulation. 



4. Holding some object causes the pedicellariae to refuse to 

 open under the usual mechanical stimuli. 



5. Long holding an object causes the pedicellaria, after re- 

 lease, to refuse to open under the ordinary stimuli. 



6. Repeated intense mechanical stimuli cause the large pedi- 

 cellariae to refuse to open under the usual stimuli. 



7. After closing the pedicellariae often open and again close 

 spontaneously, "snapping." The foregoing action furnishes the 

 condition for the succeeding one. 



There are similar variations, as we have seen in detail, in the 

 time that objects are held and in the order of the different ac- 

 tions — -the opening sometimes preceding the rising, sometimes 

 following it, etc. 



Altogether, it is clear that the reactions of the pedicellariae 

 are determined by a multiplicity of factors, giving rise to much 

 variation in the responses under given present external condi- 

 tions. 



Capture op Food. 



We have seen the action of the pedicellariae in assisting the 

 process of getting oxygen. Let us now see how the starfish pro- 

 vides the other materials for keeping the processes of metabo- 

 lism in progress. Besides oxygen, it must have a supply of pro- 

 teids and of other complicated chemical compounds, or the pro- 

 cesses making up life will cease. 



