CONFORMITY TO TYPE 259 



plication, not by division, but through the formation of 

 new ones between those already existing. The ger- 

 minal cells contain both trophoplasm and idioplasm, the 

 latter governing the growth of the former as it increases 

 itself. In this theory the thought of the continuity of 

 the germinal substance is foreshadowed. Charles Sedg- 

 wick Minot suggested that Nageli's " idioplasm " might 

 be identified with the nuclear chromatin. 



Gustav Jager in 1878 seems to have been the first to 

 express the idea that in the higher, organisms the body 

 consists of two kinds of cells which he called the " auto- 

 genetic" and " phylogenetic, " respectively, and that the 

 latter or reproductive cells are not the product of the 

 former, or body cells, but are derived directly from the 

 germ cell of the parent. 



Rauber in 1880 conceived that the effect of fertilization 

 was to convert a portion of the egg, namely, the personal 

 part, into the form of a person; the other portion does 

 not experience this effect, for it has stronger powers of 

 persistence. 



Nussbaum in 1880 also foreshadowed the idea of the 

 continuity of the germ cells, and supposed that the seg- 

 mented ovum divides into the cell material of the indi- 

 vidual and the cells for the preservation of the species. 

 These ideas remained unnoticed until Weismann's 

 theory was evolved in 1892. 



The theory of the "germ plasm" was the work of 

 Weismann and, though it may be subject to valid 

 objections, contains so large a proportion of truth that 

 it has taken a strong hold upon the thought of the day 

 and forms the basis of a large part of biological specula- 

 tion. It is essentially a cytological theory, and though 

 it follows the thought expressed in the theories preceding 

 it, that some kind of physiological units are engaged in 

 the phenomena of heredity and centres them in the germ 

 plasm which is. believed to be continuous from genera- 

 tion to generation, it progresses much further and pro- 

 poses to show the source of the germ plasm and the exact 

 location, distribution, and treatment of the units. 



