248 THE GENESIS OF SPECIES. [CHAP. 



the sexual secretions, and by their union build up the 

 embryo, each particle taking its due place, and occupy- 

 ing in the offspring a similar position to that which it 

 occupied in the parent. In 1849 Professor Owen, in 

 his treatise on " Parthenogenesis," put forward another 

 idea. According to this, the cells resulting from the 

 subdivision of the germ-cell preserve their developmental 

 force, unless employed in building up definite organic 

 structures. In certain creatures, and in certain parts of 

 other creatures, germ-cells unused are stored up, and by 

 their agency lost limbs and other mutilations are repaired. 

 Similar unused products of the germ-cell are also supposed 

 to become situate in the generative products. 



According to Mr. Herbert Spencer, in his " Principles of 

 Biology/' each living organism consists of certain so-called 

 " physiological units." Each of these units has an innate 

 power and capacity, by which it tends to build up and 

 reproduce the entire organism of which it forms a part,, 

 unless in the meantime its force is exhausted by its con- 

 tributing to the production of some distinct and definite 

 tissue a condition somewhat similar to that conceived by 

 Professor Owen. 1 



Now, at first sight, Mr. Darwin's atomic theory appears 

 to be more simple than any of the others. It has been 

 objected, that while Mr. Spencer's theory requires the 

 assumption of an innate power and tendency in each 

 physiological unit, Mr. Darwin's, on the other hand, re- 



1 Mr. Spencer, however, holds that so long as the process of growth and 

 multiplication by gemmation goes on actively, so that the aggregates and 

 their units, in a continual state of change, are not held in such constant 

 relation as to bring about an equilibrium between the form of the one and 

 the polarities of the other, the process of growth and multiplication may 

 go on without limit. 



