AS THE ELEMENTAL GERM OF AN ORGANISM 339 



nuclear masses, and of their distribution amongst the daughter- 

 cells, has given us a greater insight into the complicated pro- 

 cesses of egg and sperm maturation, and the reduction of the 

 nuclear substance thus produced. 



II. More recent Theories of Reproduction and De- 

 velopment. The new theories of generation have been worked 

 out chiefly by Darwin (IX. 6), Spencer (IX. 26), Nageli (IX. 20), 

 Strasburger (IX. 27, 28), Weismann (IX. 31-34), de Vries (IX. 

 30), and myself (IX. 10-13). The sharp antagonism which ex- 

 isted between the theories of Prefortuation and Epigenesis has 

 been diminished in these theories, in that in certain respects they 

 resemble both ; so that they could be designated from one point of 

 view, as the continuation of preformatory, and from another, as a 

 further extension of epigenetical views. The new theories, al- 

 though they hardly deserve more than the name of hypotheses, 

 differ from the old, in that they are based upon a large collection 

 of well-substantiated facts, which are to a certain extent funda- 

 mental. 



It would take too long to mention the different views of the 

 above-mentioned scientists, who, though they agree in many 

 essential points, differ considerably as to details. I will, therefore, 

 limit myself to a short description of what seems to me to be the 

 essential part of the modern theories of generation and develop- 

 ment. 



All the numerous attributes of the developed organism are 

 present in an embryonic condition in the sexual products since 

 they are passed on from the parent to the offspring. They may be 

 considered to constitute an hereditary mass (idioplasm, Nageli). 

 Each act of generation or development, therefore, does not result 

 in a new formation, or epigenesis, but produces a transformation 

 or metamorphosis of an elemental germ, or of a substance which 

 was provided with potential forces, converting it into a developed 

 organism; this, again, in its turn produces elemental germs, 

 similar to those from which it was derived. 



If the matured organism be considered to be a macrocosm, the 

 hereditary mass on the other hand represents a microcosm, com- 

 posed of numerous regularly arranged particles of material of 

 different kinds, which, each being provided with its own peculiar 

 forces, are the bearers of the hereditary properties. Just as the 

 plant or animal can be divided into milliards of elementary parts, 



