Conformity with plan 299 



of a direction, the powers of which we endeavour to investi- 

 gate ; and we find it expressed in the internal equiUbrium 

 which, within the hmits set it, effects the reparation. Vul- 

 pian's experiment, which was made about the middle of last 

 century, gave at that time the death-blow to vitalism. 

 Nowada3^s we know that it fits in completely with vitalistic 

 ideas. 



Very interesting experiments have been made on the 

 earthworm. Of these I shall mention one especially, because 

 it solves the question as to the possibility of competition 

 between two impulse-systems. Let us first cut off the head 

 of an earthworm, and a quarter of the rest of the body. Let 

 this grow on to the trunk again in the reversed position, so 

 that now a cut surface is directed forwards that normally 

 must regenerate the hind end. What is the result ? The 

 regenerated part is the missing head. Here, apparently, the 

 internal equilibrium controlling the larger portion of the body 

 has outbalanced the smaller portion, and the cut surface, 

 which is able to create either the anterior or the posterior end, 

 is compelled to meet the functional needs of the trunk. 



To the same category belongs the experiment on a small 

 crab, which has one small pincer and one large. If we cut 

 off its large pincer, the small one grows large, while in place 

 of the amputated limb a small pincer forms anew. The result 

 is a crab with reversed pincers. 



Of especial interest is the famous experiment of Herbst, 

 who succeeded in making a crab regenerate an olfactory 

 antenna in place of a stalked eye. In the course of this 

 experiment, it appeared that, when the eye was cut off, it 

 was always regenerated so long as the optical ganglion was 

 not removed. But if the whole functional building-stone 

 of the stalked eye disappears, that of the olfactory feeler leaps 

 into the gap and duplicates itself. 



All experiments made hitherto agree in this, that we 



