WHAT IS MEANT BY "A SPECIES"? 95 



separated into groups. These are what are called " species." 

 The whites are therefore not a single species, as are our 

 British swallow-tails, but a group of species, closely related 

 to one another. We find the same thing to be true with 

 regard to the blues. Though they are much alike, agreeing 

 in a variety of details of spotting and colour, yet we can dis- 

 tinguish the chalk-hill blue, the common blue, the azure-blue, 

 the Adonis blue, and others, as distinct "species " of blues. 

 Then, again, when we carefully examine our English 

 specimens of tortoise-shells, we find that there are two 

 distinct " species " — the greater and the smaller — differing 

 not only in size, but in pattern ; and when we compare 

 with these the painted lady and the peacock and the red 

 admiral, we find that there is a certain agreement of wing- 

 pattern (venation and outline) and details of shape among 

 them all, although their tints and the shape of the spots 

 and bands of colour differ. These different species " hold 

 together" just as the whites do and just as the blues do. 

 Naturalists have met the need for expressing this similarity 

 of a number of distinct species to one another by introducing 

 the term " genus " for such a group. In fact we arrange 

 several species into a " genus." The "genus" is a " kind," 

 but a more comprehensive " kind," than is a species. The 

 species is an assemblage of individuals closely alike to one 

 another ; the genus is a group of species which are more 

 like to one another than any of them are to other 

 species. 



Naturalists give to every genus a name, and also a name 

 to each species in the genus. Since we naturalists want 

 to know what butterflies or other species of animals and 

 plants are found in other countries, and to be sure that we 

 all (whatever our native language may be) mean the same 

 thing by a name, Latin names are given to the genera 

 and the species, and are necessarily used when one wishes 

 to be sure that one is understood. The greatest trouble 



