History of the Theory of Heredity. 17 



5. The new organism, whether produced sexually or 

 asexually, is essentially like its ancestors, although it 

 may be quite different from its immediate ancestor, as in 

 cases of alternation. 



6. Organisms produced from fertilized ova differ in 

 the following points from those produced asexually: 



a. As a rule the development of the egg embryo is 

 indirect, and a more or less complicated metamorphosis 

 or alternation of generations must be passed through be- 

 fore the adult form is reached, and the circuitous path 

 thus traversed bears a resemblance to the line of evolu- 

 tion of the species. An organism formed asexually trav- 

 erses only so much of this path as remains to be traversed 

 by the organism which gives birth to it. 



1). Reversion, or the appearance of characteristics not 

 exhibited by the parents, but inherited from remote an- 

 cestors, is not at all unusual in egg embryos, but it is 

 more rare in those produced asexually. 



c. New variations, or features which are not inner- . 

 itcd, appear continually in organisms produced from fer- 

 tilized ova, and they may be transmitted either sexually 

 or asexually to future generations, thus becoming estab- / 

 lished as hereditary race-characteristics. Hereditary vari- 

 ations are extremely rare in organisms produced asexually. 



7. The ovum and the male cell are homologous with 

 each other, and are morphologically equivalent to the 

 other cells of the organism. We must therefore believe 

 that their distinctive properties have been gradually ac- 

 quired, and that their specialization has been brought 

 about by the action of the same laws as those in accord- 

 ance with which the other specializations of the organism 

 have been produced. 



8. Changed conditions do not act directly, but they I 

 mse subsequent generations to vary. 





