46 Journal of Entomology and Zoology 



reactions of starfish in considerable detail. In general the star- 

 fish rights itself by twisting about two or three of its- rays until 

 the suckers on the ventral side have a firm hold of the supporting 

 surface and by controlling the twisting movement the body is 

 turned over. In this it is necessary that all five arms do not make 

 the attempt at once to bring the animal into a ventral position. If 

 five or four arms should work at once the animal could not turn 

 over. There must be some coordination between the arms as is 

 seen when the circum-oral nerve is cut. In this case the coopera- 

 tion of the arms ceases. A single arm removed from the rest can 

 right itself. These experiments seem to show that the central 

 nerve ring acts merely as a conductor of impulses. The ventral 

 side of the starfish seems to be positively stereotropic. 



If one arm of a starfish is stimulated the animal moves away 

 in a direction opposite to the stimulated arm. This looks like 

 intelligence, but when one arm is stimulated the tube-feet on this 

 arm draw in ajid according to the parallelogram of forces, a move- 

 ment away from the point of stimulation will take place. When 

 the starfish is stimulated as a whole the spines and pedicellariae 

 wave about and the jaws snap time and again. A separate exter- 

 nal stimulus is not necessary for each opening or closing of a pedi- 

 cellaria. Mechanical stimuli that are strong enough always cause 

 them to attack. Very light mechanical shock often produces no 

 efi'ect even if repeated. There are some responses to food rather 

 than defensive movements, a nutrient juice causes the pedicellariae 

 to advance and open. Pedicellariae are often opened for attack. 

 If another starfish brushes against it, even when one of the indi- 

 vidual's own rays cross, the pedicellariae may be advanced. 



If closed pedicellariae are stimulated they must first be stimu- 

 lated to open before they will attack. Any stimulus which causes 

 the pedicellariae to rise will when repeated cause them to open. 

 Most stimuli which cause the pedicellariae to withdraw also cause 

 them to close. The larger pedicellariae are usually less inclined 

 to hold objects for a long time. Starfish seem to hold objects for 

 a longer time than sea urchins. 



In starfish the pedicellariae seize and hold each other as well 

 as other objects. If a small bit of the body of a starfish, bearing a 

 single spine be cut from the rest, the pedicellariae seize any small 

 object which touches them. If the ventral nerve is cut or the 

 whole ventral side of the ray cut the pedicellariae continue to act, 

 but the cutting of the nerve acts as a stimulus. The transmission 

 of impulses seems to be by the nerve-nets over the body-wall. 



Jennings has shown that the elevation of the groups of pedi- 

 cellariae or the rosettes to attack, is dependent upon the following: 

 1. Previous mechanical stimuli; 2. Preliminary chemical stimuli; 

 3. Foregoing chemical stimuli ; 4. Cutting the radial nerve leaves 

 the rosettes in such a state that they attack more readily than 

 usual. 5. The rising of the rosettes in a central region leaves them 



