CHAPTER V 



THE CHROMOSOMES AS BEARERS OF 

 HEREDITARY MATERIAL 



The evidence in favor of the view that the chromo- 

 somes are the bearers of hereditary factors comes from 

 several sources and has continually grown stronger, 

 while a number of alleged facts, that seemed opposed 

 to this evidence, have either been disproven, or else 

 their value has been seriousl}^ questioned. We pro- 

 pose now to examine in some detail the observations 

 and experiments that bear on the chromosome theory 

 of heredity. • 



The Evidence from Embryology 



Relating to the Influence of the Chromosomes on 



Development 



It has been argued that since the sperm transmits 

 equally with the egg, and since only the sperm head, 

 consisting of the nucleus, enters the egg, inherit- 

 ance is only through the nucleus. But it must be 

 admitted that around the entering sperm nucleus 

 there may be a thin enveloping protoplasm, which, 

 however scanty, might suffice to transmit certain 

 cytoplasmic factors. Moreover, while the tail ' ^ 

 the sperm appears in some cases to be left outside tht- 



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