The Germ Plasm 311 



ing in mass, continues from generation to generation: bar- 

 ring destruction by enemies or outside agencies, Weismann 

 pointed out, such protoplasm is virtually immortal. The 

 specialized tissues of plants and animals, on the contrary, 

 while they attain their growth and development through 

 cell division as in the case of a collection of the primitive 

 organisms, reach a definite limit in their reproductive abil- 



A A A A 



Fig. 83. Relation of Parent to Offspring 



According to the older theory (lower row), the egg develops 

 into an individual (represented by the entire triangle) and a 

 portion of the body then becomes differentiated as reproductive 

 substance, the black area. In reproduction, a portion of the 

 germinal material becomes detached from the parent and de- 

 velops into a new individual. According to the later theory 

 the egg developing into an individual divides into two series of 

 cells, one of which forms the soma or body, the white area, and 

 the other the germ material, the black area of the triangles. 

 According to the older theory the body of the hen gives rise to 

 the egg. According to the newer theory, the hen, in develop- 

 ing from the egg carries some of the germ plasm within her 

 body, protecting it, nourishing it, and passing it on eventually 

 as more eggs to develop into more individuals: germ plasm has 

 a continuous history with offshoots from time to time in the 

 form of a body. 



ity: their cells have acquired mortality. Such cells make 

 up the nerves and the skin, the bones and the muscles, the 

 glands and the gristle of an animal. The only cells of a 

 mature animal that retain the immortality of the species, the 

 capacity to carry the strain forward in time, are the 

 germ cells. 



To explain the relation between the immortal germ 

 plasm and the mortal soma or body plasm, Weismann pro- 



