92 THE ZOOLOGIST. 



On seven occasions Sea-Urchins have been directly observed 

 to bite repeatedly small pebbles, but without any effect so far as 

 could be seen. The floor of that aquarium in which the twelve 

 Sea-Urchins are contained is covered to a depth of about two 

 inches with small pebbles ; and it may often be that when 

 the animals are stationary on the bottom, they are at that time 

 engaged in biting the stones ; but it is, of course, only jpossible to 

 make sure of what they are doing when they are in favourable 

 positions close to the glass.* 



On reviewing the foregoing observations on the food and 

 feeding habits of the Purple-tipped Sea-Urchin, one is struck 

 by the very great variety of its foods, which range from fish to 

 seaweeds, and excrement to shells. 



4. The Search for Food. 



Casual observation of well-fed captive Sea-Urchins, or of 

 individuals in rock-pools, might perhaps give one the impression 

 that it is the habit of a Purple-tipped Sea-Urchin to meander 

 over the bottom of the sea and simply take the food with which 

 it meets. If, however, a number of healthy and hitherto well- 

 fed Sea-Urchins are starved for four or five days, their actions, 

 when food is placed in the aquarium, show that the animals have 

 quickly become aware of its presence and that they are searching 

 for it. The first sign given by a Sea-Urchin that it has detected 

 food is the extension and eager waving in the water of those 

 tube-feet which are on the area of the animal nearest to the 

 food. Indeed, a Sea-Urchin may sometimes be seen with those 

 tube-feet which are nearest to the food extended and in motion, 

 while those which are further away are contracted and quiescent. 

 The next sign is movement, at first slow, but gradually quicken- 

 ing, in the direction of the food. This is usually accompanied 

 or followed by protrusion of the extensile mouth- membrane 

 towards the food, and alternate opening and closing of the teeth. 

 In a journey towards distant food, a Sea-Urchin will laboriously 



* It has long been known that Echinus miliaris can bore into certain 

 rocks (see F. Cailliaud, ' " Observations sur les Oursins perforants de 

 Bretagne," ' Eev. et Mag. de Zool.,' Ser. 2, T, 8, 1856, pp. 158-79) ; and there 

 is a considerable literature relating to the boring of other species, such as 

 Echinus lividus. The teeth are apparently the chief agents in boring. 



I 



