THE CONTINUITY OF LIFE 9 



each being but the temporary dress of a proliferating mass of 

 protoplasm; a detached mass of tissue, which feeds, breathes, 

 and often moves and perceives, for the better support and pro- 

 tection of the continuous living protoplasm. The soma is 

 mortal, and after a longer or shorter period loses its vitality 

 and goes to dissolution; the germ, in the restricted sense of 

 being coeval with life upon the earth, is immortal; and yet, in 

 spite of the far greater value of the latter, the two are very 

 closely associated. As the soma becomes modified, the germ 

 becomes equally so, since each germ, as it develops, repro- 



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FIG. 5. Diagrams illustrating the life cycle in unicellular and multicel- 

 lular organisms. 



The round dots represent cells. In (b) and (c) the germ cells are gray, the 

 somatic cells black. In all cases the destruction of a cell is indicated by a heavy 

 black bar placed beneath it. 



(a) Protozoan type, with equivalent gametes. The series begins with a con- 

 jugation, after which the gametes separate and a series of simple fissions follows in 

 the case of each gamete. After several generations of these, in which many of the 

 individuals produced are destroyed, conjugation again appears, completing the cycle. 



(b) Life cycle in a male Metazoan. The cycle begins with a conjugation between 

 a macro- and a micro-gamete (ovum and spermatozoon), after which there follows 

 a series of simple fissions, which differ from those of (a) in the perpetual union 

 of the components thus formed, represented here by connecting lines. There is 

 thus built up an interdependent cell-colony, the soma, shown in the fifth row from 

 the top. Certain of the somatic cells become microgametes (^spermatozoa), destined 

 for conjugation, and capable of independent existence when separated from the 

 rest. The remaining somatic cells perish simultaneously. 



(c) Same as (b), but th'e gametes produced are macrogametes ( = ova), and the 

 soma is consequently female. The conjugation of these cells with microgametes is 

 shown in the lower row, thus completing the life cycle. The bars placed beneath 

 the completed germ cells in (b) and (c) suggest the probable proportion of accidental 

 destruction. 



duces a soma almost identical with that from which it came; 

 a result which can be explained only by supposing that each 

 germ contains a controlling mechanism, directing and de- 

 termining the development of every individual part in the 

 future soma. 



