420 



THE PREFUNCTIONAL AS CONTRASTED WITH 



If the limb of a post-larval or adult newt is amputated it will re- 

 generate, provided that the fibres of the autonomic (sympathetic) 

 nervous system are intact.^ The dorsal 

 nerve-roots can be severed and the 

 dorsal ganglia destroyed, or, the 

 ventral nerve-roots can be severed 

 close to their exit from the spinal 

 cord, without destroying the power of 

 regeneration of a limb. But if the 

 sympathetic ganglia are destroyed, 

 the power of regeneration is lost also. 

 If the nerves of the brachial or sciatic 

 plexus are simply severed, the post- 

 ganglionic sympathetic fibres are 

 thereby cut, and no regeneration 

 takes place until such time as these 

 fibres have themselves regenerated.^ 



The nervous system has been 

 found to play a similar part in the re- 

 generation of the earthworm, for the 

 nerve-cord must be present at the The morphogenetic influence of 



r T ^- • ^ ^ 1 the nervous system. The anterior 



cut surface if regeneration is to take ^^^ of an earthworm is ampu- 



place from that surface. If the tated and then an incision made 



anterior end of a worm is cut oflF, and, °^ "^^ ^'f^^^^^ ^""'^f^ ^° "^ '° 



, remove the ventral nerve-cord 



in addition, the nerve-cord is ex- from several segments. No head 



tirpated for a short distance behind is regenerated from the anterior 



1 f. . , cut surface of the trunk, but one 



the cut surface, an anterior end may ^^^ ^j-m in relation to the an- 

 be regenerated from the place where terior end of the nerve-cord. 

 the nerve-cord ends, but never from g,tS. ^^-..^f ^"' ""''■ 

 the original cut surface^ (fig. 202). 



The precise role of the nervous system in many such cases of 

 regeneration is unknown, but the example of the newt's Hmb is a 

 warning that the relation may be difficult of analysis, and that only 

 fibres of a particular component of the nervous system may be 

 involved in these morphogenetic processes. 



^ Schotte, 1926 B. 

 ^ Morgan, 1902. 



Fig. 202 



