SECONDARY SEXUAL CHARACTERS 



105 



Spiders, and Vertebrates. There are a few scattered 

 instances found in other groups, but they are rare. 

 In the lowest groups they are entirely absent, and are 



FIG. 52. Four species of beetles in which the male (to the left) has horns 

 which are absent in the female (to the right). (After Darwin.) 



not found at all in plants; or rather, if character- 

 istic differences exist in plants, they are not called by 

 this name for plants cannot see or move and there- 

 fore cannot court each other. 



