248 THE GENESIS OF SPECIES. [Chip.: 



the sexual secretions, and by their union huild up the 

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

 ing in the uflspring a simihir position to that which it 

 occupied in the parent. In 1849 Professor Owen, in 

 Ins treatise on " raithenogenesis," put forward an^tlier 

 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 

 otlier 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.^ 



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

 to be more sim])le than any of the others. It has been 

 objected, that while ^Ir. Spencer's theory requires the 

 assumption of an innate power and tendency in each 

 pliysiological unit, ^Ir. Darwin's, on the other hand, re- 



' ^Ir. Spencer, however, holds that so long as the process of giowth and 

 mu]tii»lication by gemmation goes on actively, so that the aggi'cgates and 

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

 relation as to bring about an ('(juilibriuin between the form of the one and 

 the jtolarities of the ether, th€ process of growth and multiplication may 

 go on without limit. 



