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



one, lateral and downwards, till the animal assumes 

 its normal position with its oral pole against the 

 perpendicular tank wall. So considerable is the 

 rotation in the downward direction, that the normal 

 position is generally attained before one complete 

 lateral, or equatorial, rotation is completed. 



The result of this experiment, therefore, implies 

 that the righting movements are due to something 

 more than the merely successive action of the seiies 

 of feet to which the work of righting the animal 

 may happen to be given. The same conclusion is 

 pointed to by the results of the following experi- 

 ment. 



A number of vigorous Echini were thoroughly 

 shaved with a scalpel over the whole half of one 

 hemispliere, i.e. the half from the equator to the 

 oral pole. They Avere then inverted on their ab-oral 

 poles. The object of the experiment Avas to see 

 what the Echini which were thus deprived of the 

 lower half of three feet-rows would do when, in 

 executing their righting manoeuvres, they attained 

 to the equatorial position and then found no feet 

 wherewith to continue the manoeuvre. The result 

 of this experiment was first of all to show us that 

 the Echini invariably chose the unmutilated feet- 

 rows wherewith to right themselves. Probably this 

 is to be explained, either by the general principle 

 to which the escape from injury is due — viz. that 

 injury inflicted on one side of an Echinoderm 

 stimulates into increased activity the locomotor 

 organs of the opposite side, — or by the consideration 

 that destruction of the lower half of a row very 



