416 MIND IN EVOLUTION CHAP. 



parts still retain powers which show that their mutual de- 

 pendence is still far from complete. The most remarkable 

 of these powers is that of Regeneration, which, as is well- 

 known, diminishes roughly in proportion as organisation 

 advances. For example, among Worms, it is common to 

 find Regeneration not only of the tail, but even of the 

 head. 1 No Vertebrate could imitate this feat of growing 

 its head anew, but the lower Vertebrates retain a con- 

 siderable though diminished power of regenerating lost 

 limbs and other organs. Thus, the larval Salamander 

 regenerates the lens of the eye from the posterior layer of 

 the iris. 2 The Salamander can also regenerate an am- 

 putated limb, if the bone is cut across, but not if it is 

 exarticulated. These powers however are by no means 

 common to all the lower Vertebrates the frog's limb, for 

 example, would merely heal without growing again and 

 are, I imagine, wholly lost in the higher class of birds 

 and mammals, where the power of regeneration is confined 

 to that fresh growth of the adjacent tissues which we are 

 familiar with in the healing over of a wound, or in the 

 mending of a bone. 



As the loss of regenerative power points to a growing 

 centralisation of the vital functions, so also does the 

 gradual loss of independence on the part of the lower 

 nerve-centres point to the growing centralisation of the 

 nervous system. In passing from the higher to the lower 

 vertebrates, the relative independence of the spinal re- 

 flexes is well marked ; but it is as nothing to the powers of 

 separate nerve centres among the higher Invertebrates. 

 Thus, the loss of the hind quarters does not prevent a 

 bumble bee from continuing its meal, nor an ant from 

 persisting in a battle. 3 Wasmann mentions cases of an ant 

 or wasp fighting with its own severed limbs. 4 On the 

 other hand, according to Forel, 5 the severed head of an ant 

 still distinguishes a friend from an enemy. On the same 

 authority we learn that crickets deprived of the cerebral 

 ganglia can be stimulated by touch to oviposition. At 



1 See e.g. Wilson, op. tit., p. 325. 2 Wilson, p. 329. 



3 Wasmann, Instinct und Intelligent, p. 93. 4 Ibid. 



6 Aper$u de Psychologie comparee, Anne'e psychologique, 1895, p. 25. 



