THE FEEDING HABITS OF THE SKA-URCHIN. 89 



It has been said that the Sun- Star (Solaster papposiis) is 

 poisonous to some animals,* but the following observation 

 suggests that the rays at least do not injure a Purple-tipped 

 Sea-Urchin which eats them. A portion (8 mm. in length) of a 

 ray was removed from a Sun-Star on August 6th, 1915, in the 

 course of certain experiments upon the capacity for ray- 

 regeneration in that asteroid, and the amputated ray was then 

 (10.30 a.m.) immediately given to a little Sea-Urchin of 10 mm. 

 in diameter. The Sea-Urchin began at once to eat the ray, 

 and it was engaged in its meal, at the place where it began it, 

 until 11 a.m. on the 8th, by which time no fragment of the ray 

 could be discovered. The Sea-Urchin appeared to suffer no 

 ill-effects, and is still (February 26th) alive and well. 



The Sea-Urchins will devour relatively large quantities of 

 skeletons of echinoderms, just as they will devour shells and 

 exoskeletons of crustaceans. On July 29th the end portions (each 

 about 33 mm. in length) of two rays of a Common Starfish, 

 which had previously been completely skeletonised in potash, 

 were placed on a horizontal rock close to two Sea-Urchins. 

 The latter began to eat the skeletons, and when two other Sea- 

 Urchins were placed close to them they also joined in the meal. 

 Next morning (30th) only a few tiny fragments of the white 

 skeletons were to be seen. On the same day (30th) about one- 

 third of the test of an average-sized Edible Sea-Urchin {Echinus 

 esculentiis) was broken up and thrown into the aquarium. On 

 August 2nd there were added broken skeletons of an average-sized 

 Sun- Star and of a large Purple-tipped Sea-Urchin, together 

 with the broken whelk shell already mentioned (p. 88). By 

 .August 9th none of this material was to be seen, excepting 

 several of the larger pieces of the test of the Edible Sea- 

 Urchin and the harder parts of the whelk shell, which still 

 remain uneaten. It seems probable that the spines which fall 

 from living Sea-Urchins are eaten by other Sea-Urchins — they 

 certainly soon disappear from the aquarium — but a Sea-Urchin 

 has not yet been detected in the act of eating a spine. 

 Eichelbaum, it is • interesting to note, found spines of 



*'0. A. Parkeir .(in a Not6 in the 'Zoologist' of 1881, vol. xxxix, 

 pp. 214-5) records the death of two cats, one within a quarter of an hour, 

 and the other in about two hours, after eatino- a Sun-Star. 



