96 THE ZOOLOGIST. 



experiment began six Sea-Urchins — lettered respectively A, B, 

 C, D, E, and F — were visible, A and B being attached to the left 

 side of the tank, about 2 in. from the glass, and D, E, and F on 

 the bottom between the base of the rockwork and the glass. At 

 10.30 a.m. a large, closely-tied bunch of fresh Fucus vesicalosus 

 (represented in black in the fig.) was suspended from the upper 

 margin of the tank in such a way that the widely-spreading 

 ends of the fronds almost touched the glass. Sea-Urchin C was 

 wholly occupied in biting an inverted Periwinkle, and it took no 

 part in the proceedings described below. 



Sea-Urchin A, 23 mm. in diameter, which was about 7 in. 

 distant from the seaweed, showed signs of excitement in the 

 course of the eighth and ninth minutes. It raised the lower- 

 most part of its body towards the food, holding fast to the side 

 of the tank by the tube-feet of its uppermost part ; but as it 

 found it impossible to leave the side of the tank, it naturally 

 moved very slowly further and further towards the bottom. It 

 reached the point numbered 1 on the bottom, after several 

 stoppages in its course to attempt to find a direct path towards 

 the seaweed, in 240 minutes after starting on its journey. Here 

 it remained. Sea-Urchin B, of 27 mm., also moved very slowly 

 down the side, reaching point 2 in 250 minutes. Here it too 

 seemed confused, and gave up the search. D (27 mm.), E 

 (23 mm.), and F (21 mm.) seemed to become aware of the food 

 at nearly the same time as A, that is, about the ninth minute 

 after introduction of the Fucus ; but E from the first displayed 

 the most eagerness of all the echinoids to reach the food. The 

 persistence of these three animals in mounting rocks and lifting 

 up a part of their bodies towards the inaccessible seaweed was 

 very striking, and it must here be emphasised that whenever one 

 of them reached the uppermost part of a rock it would remain 

 there for a short time, as though vainly endeavouring to find a 

 solid foothold which would enable it to reach the seaweed. D 

 moved slowly and irresolutely along the base of the rocks, and 

 then moved quickly to point 3, which it reached after 95 minutes. 

 It searched the water with its tube-feet in the way just described 

 for about one minute, and then moved slowly to 4, which it 

 reached in 360 minutes. E travelled to 5 in 9 minutes, remained 

 there for about 30 seconds, and then moved to the floor again. 



