PRESENT ASPECTS OP EVOLUTION 291 



multicellular individual like the parent. And the germ- 

 cells (eggs and spermatozoa) of volvox are immortal 

 like the protozoa. But, 2, there are nutritive, somatic 

 cells, which nourish and transport the germ-cells, and 

 after their discharge die. These somatic cells, being 

 mortal, differ altogether from the germ-cells and the 

 protozoa. The protoplasm must differ in chemical, or 

 molecular, or other structure in the two cases, and we 

 distinguish the germ-plasm of the germ-cells, resem- 

 bling in certain respects Nageli's idioplasm, from so- 

 matoplasm, which performs most of the functions of 

 the cell. The somatoplasm arises from, and hence 

 must be regarded as a modification of, the germ- 

 plasm. The germ -plasm can increase indefinitely in the 

 lapse of generations, increase of the somatoplasm is 

 limited. 



When a new individual develops, a certain portion 

 of the germ-plasm of the egg is set aside and remains 

 unchanged in structure. This, increasing in quantity, 

 forms the reproductive elements for the next gener- 

 ation. The germ-plasm, which does not form the whole 

 of each reproductive element, but only a part of the 

 nucleus, is thus an exceedingly stable substance. 

 And there is a just as real continuity of germ-plasm 

 through successive generations of volvox, or of any 

 higher plants or animals, as in successive generations 

 of protozoa. 



In certain plants there is an underground stem or 

 rootstock, which grows perennially, and each year pro- 

 duces a plant from a bud at its end. This underground 

 rootstock would represent the continuous germ-plasm of 

 successive generations ; the plants which yearly arise 

 from it would represent the successive generations of 



