CONTINUITY OF THE GERM-PLASM 127 



of Pangenesis. It is a hypothesis which would explain 

 the hereditary transmission of acquired characters. At 

 the same time it is beset by difficulties which appear 

 well-nigh insuperable. 



We will now proceed to examine another theory of 

 heredity, that of Professor Weismann. The hypothesis 

 is called * The Continuity of the Germ-plasm ', the name 

 germ-plasm being applied to the essential part of the 

 germ-cell which determines its development into an 

 individual. The word 'continuity' is employed to 

 express the theory that heredity depends upon the fact 

 that a minute quantity of this germ-plasm is reserved 

 unchanged during the development of the individual, 

 and subsequently grows and gives rise to the germ-cells. 

 Hence the germ-plasm is continuous from one generation 

 to another in unending succession, and from it the germ- 

 cells of each generation are produced. 



The germ-plasm in a germ-cell possesses such a con- 

 stitution that, placed under appropriate conditions, an 

 individual of a certain species will be produced ; but the 

 germ-cells of this individual will also contain the same 

 germ-plasm, and will therefore develop into offspring 

 which resemble the parent. Parent and offspring resemble 

 each other because both arise from the same substance, 

 although it develops later in the case of the offspring. 

 Hence everything which is predetermined in the germ- 

 cell, every blastogenic character, may be transmitted, 

 while somatogenic characters cannot be transmitted. 



The hypothesis will be rendered more intelligible if 

 we refer to Diagram //, in which the development of a 

 Metazoon, like that shown in Diagram /, is represented, 

 according to the theory of the continuity of the germ- 

 plasm. Development is complete in five stages, the 

 number of the somatic cells being doubled in every stage, 

 after their first appearance in the second. The first 

 Stage (Fig. i) is the fertilized ovum. A, the single cell out 

 of which all others are produced. It contains germ- 

 plasm from two individuals, the combination being the 

 process of fertilization. In the preparation for fertili- 

 zation and the twofold nature of the fertilized ovum 



