A LESSON IN CLASSIFICATION. 103 



3. In the structure of the second segment of the body 

 of the larvae, etc. 



Such differences are used to distinguish genera. The 

 swallow-tails belong to one genus, the genus Papilio ; and 

 the cabbage butterflies to another, to the genus Pieris. 

 Make a list of the characters which distinguish these two 

 genera. 



Every species has two names, the name of the genus 

 to which it belongs, and its own specific name. A man has 

 two names, a surname and a given name. The surname 

 corresponds to the name of the genus ; the other, to the 

 name of the species. Just as there may be several John- 

 sons (John, Henry, and Eleazar), so there may be several 

 Papilios, Papilio asterias, Papilio troilus, Papilio turnus, 

 etc. The surname serves to locate the man among the 

 Johnsons ; the generic name Papilio locates the butterfly 

 among the swallow-tails. And just as the name John 

 tells which Johnson is meant, so the name asterias tells 

 which Papilio is meant. Observe that the names are 

 written, as men's names are written in a directory, sur- 

 name first. Which species of the genus Papilio have you 

 had for comparison ? 



The Family. Get, for comparison with these, one of 

 the small, thick-set, swift-flying "skipper" butterflies, 

 which rest with wings thrown backward until the costal 

 margins of the two pairs are side by side. Compare and 

 observe the marked difference in form, a difference 

 of the kind used to distinguish families. This skipper 

 butterfly is not only of a distinct species and genus, but 

 its diverse form shows a relationship still more remote. 

 It is of a different family, the family Ifesperidce. The 

 genera Papilio and Pieris are members of the family 

 Papilionidce. Make a list of the characters which dis- 

 tinguish these two families. 



