CHAPTER IX. 



THE CELL AS THE ELEMENTAL GEEM OF AN OEGANISM 

 (THEOEIES OF HEREDITY). 



WE are forced to the conclusion, that the cell is a highly or- 

 ganised body, composed of numerous, minute, different parts, and 

 that hence it is in itself to a certain extent a small elementary 

 organism, when we consider, that it is capable of executing move- 

 ments, and of reacting in a constant manner to the most various 

 external stimuli, which may be chemical, mechanical, or caused by 

 heat or light; and further that it can execute complicated chemical 

 processes and can produce numerous substances of definite com- 

 position. 



This idea is still more impressed upon us, when we take into 

 account the fact, that egg- and sperm-cells form by their union 

 the elemental germ which develops into an organism, the latter 

 reproducing on the whole the attributes of the parents, even often 

 to the most insignificant characteristics. Hence we must conclude, 

 that the egg- and sperm-cells possess all the constituent proper- 

 ties which are necessary for the production of the final result of 

 the developmental process. It is true that these properties elude 

 our perception, but that they are anything but simple, is evident 

 from the complex composition which is attained by the final 

 product of development in the highest organisms. The sexual 

 cells must therefore, of necessity, possess a large number of attri- 

 butes and characteristics, which are concealed from us, but whose 

 presence renders the formation of the final product possible. These 

 hidden or latent properties, which only gradually become evident 

 during the process of development, are called fundamental con- 

 stituent attributes. These attributes, taken collectively, to a 

 certain extent foreshadow or potentially determine the matured 

 organism. 



At a certain stage of their development, when they are simple 

 cells, all organisms are extremely alike. The ova of man, of ro- 

 dents, of ruminants, and even of many invertebrate animals, do not 

 differ from one another in any essential points ; they resemble one 



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