THE CONTINUITY OF LIFE n 



primordial germ-cells, differently marked in the diagrams, 

 which seem to retain the general qualities of the first egg-cell 

 and to resist the tendency to specialization seen in the others. 

 From these the final germ-cells develop, small and mobile in 

 the case of the male, large and provided with yolk in the case 

 of the female. These, liberating themselves from the soma, 

 unite in pairs to form another cycle like the first, while all the 

 generations of the somatic cells are sooner or later brought 

 to an end simultaneously, the death of the individual. 



This organic connection between the cells, which constitutes 

 the essential difference between unicellular and multicellular 

 organisms, has its advantages as well as its disadvantages. 

 The chief among the first is the great power of differentiation 

 among individual cells or cell-groups, with the resultant di- 

 vision of labor; a great disadvantage lies in the fact that 

 through this very specialization of function, any vital accident 

 occurring in one part drags down to death all the other cells 

 of the organism. The germ-cells alone are the immortal 

 parts, the continuous principle which survives the destruction 

 of the soma, and each contains within itself, expressed in the 

 form of an ultra-complex mechanism, the ability to reproduce 

 in its cell descendants every detail of the soma from which 

 it originated. 



In this is seen the primary value of the soma, which be- 

 comes clear when taken in connection with the struggle on the 

 part of nature to develop as much protoplasm as possible. 

 The soma is a mass of protective cells, capable of a high 

 degree of specialization, and thus able to adapt itself in accord- 

 ance with the needs of every environment in which it is 

 possible for organic beings to exist. Even its death is an 

 adaptation, for by this means new and perfect somata are con- 

 stantly taking the place of those whose usefulness as guardians 

 of the germ-cells has become impaired by the inevitable injury 

 to which organisms are constantly exposed. Life is con- 

 tinuous in the germ-cells from generation to generation and 

 has been carried into all environments and protected and 

 multiplied through a constant succession of perishable somata. 



