358 ORGANIC GROWTH sec. 



former the motion after its reappearance attained sooner than 

 in the others to the rapidity which it had in the entire 

 animal — in fact, in many of the pieces without sense-organ, or 

 in fragments of these, the motion remained permanently 

 slower, as well as more irregular, than it was in the entire 

 animal. Most of the pieces, however, recovered completely, and 

 halves of Beroe containing no sense-organ usually soon swam 

 about exactly like an entire animal, and also in the same direc- 

 tion as the latter, the mouth forwards, they reacted to stimuli 

 exactly as entire animals, and seemed to be not at all inferior 

 to these in psychical capabilities. Such a piece had also the 

 power, like an entire animal, of stopping at pleasure the 

 motion of any one of the rows of plates. As in the entire 

 animal, the movement in the pieces as a rule commenced at 

 the edge nearest the sensory-pole, and proceeded towards the 

 mouth. But in rare cases I saw the movement commence 

 somewhere in the course of the row of plates. 



The difference between the results of experiments on Beroe 

 and those on Medusae shows that in the latter the localisation 

 of nervous action has proceeded further than in the former, a 

 conclusion with which my histological observations are in 

 perfect harmony. In Beroe the total body-surface is in a 

 still higher degree to be regarded as the brain, the accumu- 

 lation of ganglion-cells in the sensory-pole in Beroe is more 

 gradual and less distinctly defined than in the marginal bodies 

 of Medusae. In the latter I was able to stop all movement by 

 pricking with a needle any one of the eight nerve-centres, in 

 Beroe this is not possible. In Beroe separated portions soon 

 begin to move again, in Aurelia aurita it was first necessary that 

 a vicarious nerve-centre should be formed from cells which had 

 either lost or almost lost the function of central nerve-cells. 

 Hence motion reappeared in Aurelia rarely, and always in a 

 manner which exhibited most clearly the clumsiness of the 

 action of the apparatus at first. In Beroe, on the contrary, 



