EMBRYOLOGY 



237 



unbroken for an indefinite time, thus constituting the race. At inter- 

 vals they may proHferate off from themselves other cells that are tempo- 

 rary, in the form of a body in which the germ cells are lodged. While in 



!st&EN. 



End.GEN. 



Jrcf.GEN. 



4fh.6eN. 



Fig. 187. — Diagram illustrating the conception of the independence of the germ cells 

 in a parthenogenetic animal. The shaded areas (G) represent the germ cells, the white areas 

 ((S) the somatic cells. In each generation germ cells give rise to both germ cells and som- 

 atic cells. Somatic cells never give rise to germ cells. Somatic cells can not therefore 

 transmit anything to the germ cells and the next generation merely by descent. (Modified 

 from drawing by P. 0. Okkelberg.) 



this body some of the germ cells escape and form new bodies around 

 themselves. Some germ cells remain in the old body until it is too late 

 to escape; but ordinarily some of them escape before that time, and 



Parents 



Offspring 



Fig. 188. — Scheme illustrating the conception of the independence of the germ cells 

 In animals reproducing by the bisexual method. The shaded areas (g) represent germ cells, 

 the white areas (s) somatic ceils. In each generation fused germ cells give rise to both 

 somatic cells and germ cells. Somatic cells never give rise to germ cells. Somatic cells 

 therefore can not transmit anything to germ cells and the next generation merely by 

 descent. (Modified from drawing by P. 0. Okkelberg.) 



provide descendants that may live on forever. The germ cells are thus 

 a continuous reserve supply out of which temporary bodies are at intervals 

 developed. This idea is contained in the diagrams in Figs. 187 and 188. 

 The body cells are not, therefore, on a par with the germ cells ; for germ 



