Jarovisation 



See Vernalization. 



Jordanon 



A Microspecies (q. v.). 



Jordan's Rule 



The generalization that fishes living in waters of low 

 temperatures tend to have more vertebrae than do those in 

 warm waters. 



Jurassic 



A geological period in the Mesozoic era which began 

 about 165 million years ago and lasted about 30 million. 



197 



