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 



