308 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



seem suMlcient to prove the fact of a general co- 

 ordination among the feet ; but further reflection 

 will show that it is not so. For the feet being all 

 arranged in rec>u]ar series, when one row begins to 

 effect the rotation of the globe, it may very well be 

 that its further rotation in the same direction is due 

 only to the fact that the slight tilt produced by the 

 jmlling of the tirst feet in the series A, B, C gives 

 the next feet in the series D, E, F an opportunity 

 of reaching the floor of the tank; their adhesions 

 being established, they would tend by their pulling 

 to increase still furtlier the tilt of the globe, thus 

 giving the next feet in the series an oppoi'tunity of 

 fastening to the floor of the tank, and so on. In 

 order, therefore, to see whether these righting 

 movements were due to nervous co-ordination 

 among the feet, or merely to the accident of the 

 serial arrangement of the feet, we tried the experi- 

 ments which I shall now detail. 



First of all we took an Echinus, and by means of 

 a thread suspended it upside-down in a tank of 

 water half-way up the side of the tank, and in such 

 a way that only the feet on one side of the ab-oral 

 pole were able to reach the perpendicular wall of 

 the tank. These feet as quickly as possible estab- 

 lished their adhesions to the pei-pendicular wall, 

 and, the thread being then removed, the Echinus 

 was left sticking to the side of the tank in an in- 

 verted position by means of the ab-oral ends of two 

 adjacent feet-rows (Fig. 50). Under these circum- 

 stances, as we should expect from the previous ex- 

 periments, the animal sets about righting itself as 



