THE FEEDING HABITS OF THE SEA-URCHIN. 97 



It crossed the floor, and when it touched the glass at point 6 it 

 climbed quickly up, stopping for 30 minutes at point 7 to eat 

 part of a Rissoa which lay in its path. It then dropped the 

 remains of the mollusc, and mounted quickly and directly to the 

 seaweed, which it reached in 6 minutes after leaving point 7 and 

 142 minutes after starting. Sea-Urchin F first crept away 

 behind the rocks, and, as it was believed that it had gone 

 astray, its course was not for the time being observed. At 242 

 minutes after starting, however, it reappeared from behind the 

 rocks at point 8. It traversed the rocks to 9, stayed there for 

 90 seconds with body raised and tube-feet waving; then it moved 

 down to 10, where it stopped for a few seconds; it finally reached 

 point 11 in 360 minutes. As it was now impossible to continue 

 to make detailed notes of the behaviour of the animals, the sea- 

 weed was thrown amongst the rocks between points 3, 4, and 11. 

 All the Sea-Urchins were upon the seaweed at 9.15 the following 

 morning, with the exception of C, which was still upon the 

 Periwinkle. 



5. The Positions and Postures Adopted in Feeding. 



The favourite method of feeding, if one may safely generalise 

 from observation of sixty captive examples, is to enter into 

 the heart of a bunch of seaweed, and particularly into the firm 

 " roots " of such forms as have these in thick masses, and to 

 remain ensconced there. Indeed, it is frequently to be observed 

 that a Sea-Urchin, or several clustered Sea-Urchins, will remain 

 in such a situation until the seaweed has become reduced to 

 fragments and the animals surrounded by loose heaps of faecal 

 pellets. The Sea-Urchin will bite a hole in a frond of seaweed, 

 but it usually begins at the edge or at a place where there is 

 already a break or perforation. 



A Sea-Urchin readily adapts its posture to the needs of 

 biting food which is difficult to reach. One end of a long and 

 narrow frond will often be held with spines and tube-feet 

 against the teeth, in a way which absurdly suggests the 

 smoking of a cigar, and then be gradually eaten away. In 

 the case of a firm frond projecting from an otherwise inaccessible 

 bunch, the animal will raise itself on its rim, so that its teeth 

 Zool. 4th ser. vol. XX., March, 1916. i 



