128 DEVELOPMENT AND HEREDITY. 



like the oi'iginal germ-like form, then the process 

 of its development could not be repeated and its 

 regeneration would be impossible. But at every 

 step in the evolution a part of the protoplasm 

 retains its original qualities, only changing its ner- 

 vous condition to a condition of greater complexity 

 of co-ordinations. In this way the original proto- 

 plasm gradually adds to itself the co-ordinations for 

 developing in each generation, first cell walls, and 

 then differentiated organs. Thus are produced parts 

 which cannot subdivide in particles, and cannot, by 

 reacting to the external forces, repeat in each par- 

 ticle the development of the species. The differ- 

 entiated organs, for some essential reason that we 

 will consider later, have not the power of enduring 

 indefinitely, and therefore together form that part 

 of the organism which dies. At one extreme of 

 the scale we see the new-born protozoa bursting 

 and casting off the dead membrane which protected 

 the protoplasm during the period of " rest " or incu- 

 bation ; at the other extreme we see the body of 

 an animal die long after it has ceased to produce 

 young. 



Professor Weismann has recently advanced a theory 

 of heredity, in which he holds the view that the 

 changes which occur in the body (soma) of an indi- 

 vidual cannot affect the germ-cells. This view is 



