72 ZOOLOGY 



Synapsis What is the purpose of the synaptic shuffle and its 



viability resulting phenomenon, the crossing over of factors 

 otherwise linked ? Evidently, in heterozygous or cross- 

 bred races, it increases variability, and provides for the 

 almost endless variety of living types, furnishing the 

 material for natural selection. Through such means 

 Nature furnishes, as it were, innumerable keys to un- 

 lock the doors of opportunity. Many, indeed most, 

 must fail ; but many succeed, and these fill the world 

 with variously adapted forms of life. 



