AUGUST WEISMANN. vll 



indeed as he says in the preface of this book, it is " a mirror of the 

 course of my own intellectual evolution." 



Without attempting to analyze these different books, which 

 would require more time and space than is here available, we may 

 proceed at once to a summary of his more important contributions 

 to the theories of evolution and heredity. 



All his theories, both of heredity and evolution, center in what 

 he called the "germ-plasm," that particular part of the germ cells 

 which serves to carry over from generation to generation the in- 

 heritance factors. This germ-plasm was held by Weismann to be 

 absolutely continuous from the present generation back to the 

 earliest generations of living things ; it was absolutely distinct from 

 the somatoplasm of the body and the latter could never become 

 germ-plasm ; it was almost perfectly stable undergoing practically 

 no changes except such as came from the mixing of different kinds 

 of germ-plasm (amphimixis) in sexual reproduction. 



.These views as to the nature of the germ-plasm underwent 

 some modification as the result of criticism. Weismann was forced 

 to admit that the distinctness and stability of the germ-plasm were 

 not absolute, but in spite of all criticism he was able to maintain 

 that the germ-plasm was relatively very distinct from other plasms 

 and very stable in organization and this is now admitted by all 

 persons acquainted with the subject. 



His views as to the separateness of somatoplasm and germ- 

 plasm, of body cells and germ cells, and the mortality of the former 

 and potential immortality of the latter, led him to regard organisms 

 in which this distinction does not exist (many protozoa and proto- 

 phyta) as potentially immortal. With a keenness of insight 

 which w^as not appreciated at the time but which has been con- 

 firmed by recent work he reasoned that " conjugation like food and 

 oxygen may be conditions of life but immortality does not rest on the 

 magic of conjugation any more than on food or oxygen." Again 

 he anticipated the most recent opinions when he held that death is 

 not a necessary correlative of life, but rather the result of higher 

 differentiation. In short, as Minot said, " Death is the price we 

 pay for our differentiation." On the other hand, his attempt to 



