HEREDITY 1 1 3 



have revealed, the chromosomes are the only phys- 

 ical bodies which might be held responsible in 

 transferring parental qualities to an offspring. 

 Upon this point scientists are agreed: we accept 

 as fact that the chromosomes are the physical 

 bearers of heredity. 



Their minute size alone makes this statement 

 seem like a gross assumption, but there is no other 

 material substance contributed by either parent 

 by means of which traits could be transmitted. 

 There is an enormous mass of technical papers 

 dealing with the size, form and changes in 

 chromosomes during fertilization which any in- 

 terested reader may consult as the source of these 

 facts. For those who do not wish to examine the 

 original sources, it may be stated that chromatin 

 grows and greatly increases in amount as each new 

 cell is produced, thus carrying to this new cell the 

 ' physical bodies which have through growth and 

 division been derived from the parental chromo- 

 somes. 



But when the next natural question is asked. 

 How do these chromosomes carry characters from 

 parent to offspring? we pass into the realm of 

 hypothesis. Darwin offered the first hypothesis 

 to explain heredity in 1868 and it is always well 

 for the student who wishes to understand the vari- 

 ous views that have been advanced to begin his 



