72 University of California Puhlications in Zoology. [Vol. 4 



eellariae without farther stimulation. These differences are 

 doubtless due to different physiological states in the different 

 rosettes, resulting from different past histories. They seem not 

 due to different ages of the rosettes, since contiguous rosettes 

 at the same level of the ray may show these differences. 



Even in the same rosette, after it has risen, some of the pedi- 

 cellariae may be open, while others remain closed. 



Let us suppose that a rosette has risen, but that the jaws 

 have not opened, as we often find to be the case. What will now 

 cause the pedicellariae to open ? 



This is usually brought about by rubbing or jabbing the 

 rosette ; usually all of its pedicellariae open at once, both those 

 directly struck, and those not touched. Any stimulus that causes 

 the rosettes to rise will, when repeated, cause the pedicellariae 

 to open. If the rising has been caused by a chemical stimulus, 

 a light mechanical stimulus following the chemical causes the 

 opening. 



If in an extended rosette in which the pedicellariae are still 

 closed we try stimulating the individual pedicellaria by touching 

 its outer surface with a fine hair or bristle, it is usually not possi- 

 ble to get it to open alone. As a rule the immediately contiguous; 

 pedicellariae open first, the stimulation evidently being trans- 

 mitted through the underlying fleshy mass. The pedicellaria 

 directly stimulated then opens a moment later. In rare cases, by 

 stimulating very lightly the outer surface of a single pedicellaria. 

 it alone may be induced to open. 



The large solitary pedicellariae are usually readily induced 

 to open by lightly touching several times the outer surface. The 

 jaws then gap widely and remain open for sime time : — often for 

 as much as five minutes. When several of these large pedi- 

 cellariae are near together, a stimulus on the outer surface of 

 one causes its neighbors to open simultaneously with it. A stim- 

 ulus on the gills or the body surface near the large pedicellariae 

 usually causes them to open and bend toward the spot stimulated. 

 But sometimes they merely bend over toward the spot, and wait 

 for a new stimulus before opening. A large pedicellaria may 

 likewise be caused to open by rubbing the side of its stalk, or even 

 by thrusting a fine-pointed glass rod into the angle between the 

 lower parts of the two jaws. 



