182 DEVELOPMENT AND HEREDITY. 



power of reproducing itself and developing new 

 tissue of the same kind, but only of the same 

 kind, and no other. Muscle tissue will not produce 

 epidermis, nor will glandular tissue produce muscle. 

 We see thus that there is in each tissue but a single 

 plan of development, — a single set of co-ordinations 

 which guide and limit the activity of the tissue. 



There is still another example of the singleness of 

 plan found in the reproduction of lost parts among 

 the lower animals, such as the reproduction of the 

 lost tail of a lizard, or the lost leg of a newt. There 

 is not, in these cases, a simple addition of new tissue 

 layer by layer on the wounded stump ; but the part 

 to be reproduced is formed first in embryonic size 

 and condition, and passes thus through nearly the 

 same phases of growth that were followed by the 

 original part, repeating the original single plan of 

 growth. 



