38 



Where the variations in two organs are per- 

 fectly correlated ^ = -j- i . 



Where two organs vary entirely independ- 

 ently r^ o. 



Value of r the same for any given pair of 

 organs through )ut the species, Weldon. 



Value of ;' higher between homologous parts 

 and between adjacent parts, than between 

 parts not so related, Weldon, Thompson. 



(3) Parallel variation. 

 Peacocks. 

 Nectarines. 



d. Laws of Racial Variation. 



Specific characters more variable than generic. 



" A part developed in any species in an extraor- 

 dinary degree or manner, in comparison with 

 the same part in allied species, tends to be 

 highly variable." 



Secondary sexual characters. 



Usually confined to males. 



Often developed in an extraordinary manner 



or degree. 

 Highly variable. 



Law of " equable variation." 



" The species of the larger genera in each coun- 

 try vary more frequently than species of the 

 smaller genera." 



'• Wide ranging much diffused and common spe- 

 cies vary most." 



Crossing leads to variability. 



