Recapitulation and Conclusion. 319 



vary as well as those born from fertilized seeds, although 

 bud variations arc extremely rare as compared with seed- 

 ling variations. 



In any attempt to frame an hypothesis of heredity we 

 must therefore recognize all the following facts : that 

 the two reproductive elements are homologous, and that 

 their functions were originally alike; that the possibility 

 of parthenogenesis, together with many other well ascer- 

 tained facts, shows that their functions are not alike, in 

 the higher organisms, at present; that their present 

 functions are due to divergent specialization or physio- 

 logical division of labor; that variation is possible with- 

 out sexual union, but that the introduction of a male 

 element in reproduction greatly increases the frequency 

 of its occurrence. 



Among the unicellular organisms variability is provi- 

 ded for by conjugation, or the fusion of two entire indi- 

 viduals so that the new generation is derived from a 

 compound germ which contains particles to represent all 

 the parts of thevbody of each parent. In the metazoa 

 and the many celled plants the reproductive bodies are 

 localized and they are single cells, and there must there- 

 fore be some mechanism or organization in virtue of 

 which they represent cells from all parts of the body, 

 and thus provide fur further variation. 



These various considerations have led us to believe 

 that each cell of the organism inherits from its unicel- 

 lular ancestors the power to throw off cell germs or 

 gemmules; that these germs penetrate to all parts of 

 the body, and that those which thus reach the devel- 

 oping reproductive elements insure variation, in the 

 next generation, in the cells which they represent: that 

 originally the two sexual elements were alike in function; 

 that each inherited from the fertilized ovum of the pre- 



