422 



THE AMERICA X XATURALIST [Vol. LV 



the outer margin being fairly constant features. It is 

 usually thick and rather fleshy in appearance. The dis- 

 tribution of hair on the surface of the ear is similar to 

 the normal. 



EXPERIMEXTAL Ix VESTIGATIOlSr 



The Mutant Oiit-cros.si'd. — The first two experiments 

 showed immediately tliat tlie character " short ears " is 

 recessive and that it is not sex-linked. Seven crosses 

 were made between short-eared males and a number of 

 long-eared females which were taken from sources other 

 than the Lathrop stock or from Lathrop strains which 



