OBJECTS CARRIED BY THE SEA-URCHIN. 449 



certainly seem to be more need of protection for the smaller 

 than for the larger individuals, because an animal which might 

 easily manage to eat a Sea-Urchin of 10 mm. possessing com- 

 paratively small spines, might not be able to eat one of 30 or 

 40 mm. with a formidable mass of spines. 



It was to be noted that if any objects at all were carried by 

 a Sea-Urchin, these objects were nearly always held so that 

 they covered the anus of the animal. This was well seen in the 

 case of the large individuals, and was particularly striking when 

 one of them carried only one or two pebbles. In one hundred 

 and ten successive examinations of loaded Sea-Urchins it was 

 found that in ninety-six cases the materials were so arranged 

 that they covered the anus, while in the majority of the other 

 fourteen cases they were carried close to it. It would seem that 

 while a Sea-Urchin gradually loses the habit of carrying a mass 

 of objects, it retains that of carrying sufficient to cover the anal 

 parts, and this habit (observed in other examples besides these 

 eleven) seems to demand an explanation. 



When a Sea-Urchin is watched as it creeps with its load 

 along a horizontal surface, a sufficient explanation would seem 

 to be that the animal instinctively places the objects on the part 

 where they are most easily carried, that is, on the flattened 

 upper pole of the animal. But this explanation is seen to be 

 inadequate when it is remarked that Sea- Urchins carrying 

 materials are to be seen in a vertical position quite as often as 

 they are in a horizontal one, and that it has several times been 

 observed in the tank that a Sea-Urchin in a vertical position 

 will proceed to transfer to its anus a stone laid upon the upper- 

 most part of the animal. The true explanation may perhaps be 

 that in the living* Sea-Urchin the well-marked anal region, with 

 its palisade-like circle of spines, readily catches the eye of a 

 predatory fish, and must therefore be hidden. Again, when the 

 Sea-Urchin is defascating, the successive pellet-like fseces attract 

 attention as they fall down the animal after being thrown out of 

 the anus, and the presence of a pebble or other object (which is 

 usually held, by the spines or tube-feet or both, at a little height 



* In a dead Sea-Urchin, owing to the irregular way in which the spines 

 are disposed, this eye-like anal region is by no means so conspicuous as it is 

 in the healthy living animal. 



