WHAT IS MEANT BY "A SPECIES"? 93 



means a group held together by kinship, and it may be a 

 larger or a smaller group held together by a close kinship 

 or by a more distant one. " Sort," again, will not serve 

 our purpose as an English translation of " species." For, 

 although " a sort " implies a certain selection and similarity 

 of the things included in the "sort," the amount of 

 similarity implied may be very great or it may be in- 

 definitely vague and remote. Hence naturalists have to 

 stick to the word "species," and to use it with a clear 

 definition of what they mean by it. 



Suppose we get together a large unsorted collection 

 many hundred "specimens" or individuals of the 

 common butterflies of England. Then, if we look them 

 over, we shall find that we can pick out and arrange the 

 specimens into definite groups, according to their colour- 

 pattern. We find that the kinds which we readily 

 distinguish are called in English the swallow-tails, the 

 whites, the sulphurs, the clouded yellows, the tortoise- 

 shells, the peacocks, the red admirals, the painted ladies, 

 the gatekeepers, the meadow browns, the heaths, the 

 coppers, and the blues. There might be others in such 

 a collection, but that is enough for our purpose. On 

 examining the specimens closely, we find that the colour- 

 markings and " venation " or network by which the wings 

 are marked and the shape of the wings, body, and legs 

 of all the specimens of the swallow-tails are almost exactly 

 alike, and unlike those of any of the others. We shall 

 find if we have a dozen or two specimens that there is a 

 slight difference in the pattern, size, and colour of wing of 

 some of the swallow-tails, dividing them into two groups, 

 which we soon ascertain to be the males and females ; but 

 this is so small a difference that we may ignore it. The 

 swallow-tail is obviously and at once distinguished from 

 any of the other butterflies in the collection by its colour- 

 pattern and shape. So also with the others, there will be 



