The Making of Species 



17. Why differences in the nature of the food 

 administered to the larvae of ants determines 

 whether these shall develop into sexual or neuter 

 forms. 



1 8. Why the application of heat, cold, etc., to 

 certain larvae affects the nature of the imago, or 

 perfect insect, to which they will give rise. 



19. Why the females in some species lay eggs 

 which can produce young without being fertilised. 



20. Why some species exhibit the phenomena 

 of sexual dimorphism, while others do not. 



21. In addition to all the above, a satisfactory 

 theory of inheritance must account for all the 

 varied phenomena which are associated with the 

 name of Mendel. It must explain the various 

 facts with which we have dealt in the chapter on 

 hybridism, why some species produce sterile 

 hybrids when intercrossed, while others give rise 

 to fertile hybrids, and yet others form no offspring 

 when crossed ; why the hinny differs in appear- 

 ance from the mule, etc. 



22. It must explain all the facts which consti- 

 tute what is known as atavism. 



23. It must account for the phenomenon of 

 prepotency. 



24. It must explain the why and the wherefore 

 of correlation. 



25. It must tell us the meaning of the 

 results of the experiments of Driesch, Roux, 

 and others. 



136 



