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 seriously questioned. We pro- 
pose now to examine in some detail the observations 
and experiments that bear on the chromosome theory 
of heredity. 
Tue 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 of 
the sperm appears in some cases to be left outside the 
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