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REGENERATION IN FLATWORMS 



Experiments with flatworms show the regeneration of a complete animal from a seg- 

 ment. If the head is removed, if the hind part is removed, if a section is cut from the 

 middle, a complete animal will be regrown. The shaded areas represent the new 

 growth 



removed. A lobster will regrow a complete new claw. Salamanders re- 

 generate complete tails and legs. The glass snake (which is really a lizard 

 with reduced legs) leaves his tail behind when it is grasped, but then grows 

 himself another (see illustration, p. 230). 



At the other extreme are more highly specialized warm-blooded organ- 

 isms. We can regrow skin, or bone, or connective tissue. When nerve and 

 brain cells are injured, however, they are replaced by scar tissue. Scar 

 tissue closes a gap, but it does not have the characteristic of nerves, nor does 

 it do the work of the destroyed nerve cells. 



Plants usually heal wounds more directly: exposed cells dry up. In many 

 cases, however, regeneration or healing may be observed. In some species, 

 even a small piece of leaf or stem may regenerate leaves and roots and, under 

 suitable conditions, a complete plant (see illustration, p. 231). When the 

 bark is scraped from a tree, and the growing layer is exposed, proliferation 

 of cells results in a mass of callus. This covers the wound but does not con- 

 tinue to grow. 



229 



