84 THE ZOOLOGIST. 



wholly or partially eaten. The long halves of four of the legs 

 of Hyas, together with their soft contents, were eaten, and the 

 other halves then abandoned. It may also be remarked that 

 on three other occasions when Sea-Urchins ate halves of limbs, 

 they afterwards placed the uneaten halves on their upper surfaces 

 amongst the other foreign objects with which the Purple-tipped 

 Sea-Urchins so frequently load themselves. A carapace, 48 mm. 

 in length, of a dead Common Spider-Crab was given to a Sea- 

 Urchin of 38 mm., and was nibbled around its edge. 



The avidity with which the Purple-tipped Sea-Urchin will 

 feed upon an exoskeleton which has been moulted by a shrimp 

 or prawn is very remarkable ; indeed, it has now become my 

 practice to give all such cast exoskeletons to the Sea-Urchins as 

 part of their food, and they are very seldom refused. Out of 

 thirty-three consecutive exoskeletons of shrimps, varying from 

 45 to 75 mm. in length (excluding the antennae), all except two 

 were at once taken by the Sea-Urchins to which they were 

 presented, and the two exceptions were afterwards eaten by 

 other Sea-Urchins. It should be understood that the exo- 

 skeletons are not eaten only by starving Sea-Urchins ; they are 

 eagerly taken by well-fed individuals which immediately before 

 have been devouring seaweed. A Sea-Urchin of 42 mm., 

 abundantly supplied with seaweed, ate each of the fifteen suc- 

 cessive exoskeletons which were given to it in the course of 

 thirty-one days. 



The worm-shaped faeces of the Shore-Crab, Common Spider- 

 Crab, Common Hermit-Crab, and Sea-Bullhead are eaten by a 

 Sea-Urchin whenever these are offered to it. The echinoids would 

 probably eat the faeces of almost any other marine animal. A 

 Sea-Urchin detected the presence of three faeces (of 15, 21, and 

 25 mm. in length) of a Shore-Crab when they were placed three- 

 quarters of an inch away ; and within a few minutes the animal 

 approached, and ate them. 



It has already been mentioned (p. 83) that the tube-feet and 

 spines may be used to imprison a dying Wrasse, and it may here 

 be added that these appendages are of great use in holding food 

 when the Sea-Urchin is clinging to a vertical surface. When, 

 for example, a Sea-Urchin, attached to the glass front of the 

 aquarium, is given the exoskeleton of a shrimp, it may dis- 



