The Making of Species 
17. Why differences in the nature of the food 
administered to the larve of ants determines 
whether these shall develop into sexual or neuter 
forms. 
18. Why the application of heat, cold, etc., to 
certain larve 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. 
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