448 THE ZOOLOGIST. 



were removed it picked up eight pebbles weighing 1*6 gr. in 

 eighteen minutes. Its further movements were not watched on 

 this day, but on the following morning it was found to be carrying 

 three pebbles and a fragment of seaweed weighing 0*2 gr. It 

 again picked up these objects whilst it was being weighed in the 

 small vessel of sea-water. Ten minutes after being replaced in 

 the tank it had picked up five pebbles of 07 gr. Two minutes 

 after removal of these it had picked up a piece of seaweed. As 

 in the case of the Sea-Urchin of 10 mm., this specimen was 

 always replaced in the aquarium with its mouth downwards, and 

 was watched as it picked up each object. The manner in which 

 these two small Sea-Urchins picked up fresh objects suggested 

 that removal of the materials acted as a stimulus to pick up 

 others. 



3. The five largest Sea-Urchins were placed on the floor of 

 the tank, after removal of any objects they carried. One 

 deliberately picked up a piece of seaweed and carried it in the 

 course of a few minutes to the anal region. One picked up four 

 stones and carried them to the anal region in ten minutes. One 

 picked up one pebble and carried it to the anal region in ten 

 minutes. The two largest picked up one of them one pebble, 

 and the other two pebbles, but each let its burden fall again 

 almost immediately. Next day six large Sea-Urchins were 

 deprived of any materials they carried, placed on the floor of the 

 tank, and watched for half an hour. During this time an 

 individual of 23 mm. picked up seven pebbles and a piece of 

 seaweed weighing l'l gr. ; one of 21 mm. picked up five pebbles 

 of 0*9 gr. ; another one of 21 mm. picked up eleven pebbles of 

 TO gr. ; and three of them (of 23, 27, and 27 mm.) did not pick 

 up any objects. One of the Sea-Urchins of 27 mm., which per- 

 sistently crept away to ascend the vertical side of the aquarium, 

 was replaced on the pebbles on three successive occasions, but 

 on none of them did it attempt to pick up anything. 



The evidence derived from the observation of these eleven 

 Sea-Urchins suggests that the habit of carrying foreign materials 

 is gradually lost as the animal grows bigger.* There would 



* E. Elmhirst (' The Naturalist at the Seashore,' 1913, p. 33) mentions 

 that the Edible Sea-Urchin (E. esculentus) occasionally dresses itself with 

 materials, "especially young ones." 



