94 THE ZOOLOGIST. 



Sea-Urchin A, which was 6 in. distant from the seaweed, 

 showed the customary signs of excitement almost immediately 

 after introduction of the food, and within about twenty seconds 

 had begun to move towards it. It moved a little out of the 

 direct path, as shown in the plan. It reached and began to eat 

 the seaweed in the tenth minute after starting on its journey. 

 Sea-Urchin B, which was 19 in. away from the seaweed, detected 

 the presence of the Laminaria almost immediately after A. It 

 at first went astray towards the surface of the water. At point 3 

 it turned quickly downwards again, and reached the food in twenty- 

 nine minutes after starting. C and D, which were respectively 

 19 and 21 in. away from the seaweed, showed no signs of excite- 

 ment until the twelfth minute. C then lifted itself from the 

 pebbles and moved towards the food, at first quickly and then 

 more slowly, reaching the seaweed in 160 minutes. D moved 

 excitedly, but from the first wholly in the wrong direction. 

 When it reached point 2, however, it turned downwards and 

 travelled directly towards the food, but at what time it reached 

 the latter was not observed, the only remark preserved in my 

 notes being that it passed point 2 at 110 minutes after starting. 

 The constant circulation of the water is perhaps the cause of the 

 inability of the Sea-Urchins to go directly towards distant food. 

 A Sea-Urchin of 10 mm., which hitherto had been completely 

 hidden amongst the rocks, unexpectedly made its appearance 

 after thirty minutes. This animal must have been fully 24 in. 

 distant (in a straight line) from the food, to reach which it had 

 to traverse probably not less than 4 ft. of rock surface. The 

 exact time at which it reached the seaweed is not known. On 

 the following morning two other Sea-Urchins, in addition to the 

 five mentioned above, were found on the seaweed. 



Second experiment. — The second experiment was made two 

 weeks later, the Sea-Urchins again being starved for a few days ; 

 but in this instance the seaweed was suspended from the surface, 

 and this had unexpected results. A view of the left portion of 

 the contents, consisting mainly of piles of loose rocks, of the 

 same aquarium is given in fig. 3. The reader is supposed to be 

 looking through the glass front, and also somewhat downwards 

 upon the bottom, of the aquarium, the bases of the piled rocks 

 being about 2 in. from the glass. At the moment when the 



