VARIATION UNDER NATURE 45 



as varieties, but which have all been ranked by 

 botanists as species ; and in making- this list he has 

 omitted many trifling varieties, but which nevertheless 

 have been ranked by some botanists as species, and he 

 has entirely omitted several highly polymorphic genera. 

 Under genera, including the most polymorphic forms, 

 Mr. Babington gives 251 species, whereas Mr. Ben- 

 tham gives only 112, — a difference of 139 doubtful 

 forms ! Amongst animals which unite for each birth, 

 and which are highly locomotive, doubtful forms, 

 ranked by one zoologist as a species and by another as 

 a variety, can rarely be found within the same country, 

 but are common in separated areas. How many of 

 those birds and insects in North America and Europe, 

 which differ very slightly from each other, have been 

 ranked by one eminent naturalist as undoubted species, 

 and by another as varieties, or, as they are often called, 

 as geographical races ! Many years ago, when comparing, 

 and seeing others compare, the birds from the separate 

 islands of the Galapagos Archipelago, both one with 

 another, and with those from the American mainland, 

 I was much struck how entirely vague and arbitrary 

 is the distinction between species and varieties. On 

 the islets of the little Madeira group there are many 

 insects which are characterised as varieties in Mr. Wol- 

 laston's admirable work, but which it cannot be doubted 

 would be ranked as distinct species by many entomo- 

 logists. Even Ireland has a few animals, now generally 

 regarded as varieties, but which have been ranked 

 as species by some zoologists. Several most experienced 

 ornithologists consider our British red grouse as only a 

 strongly-marked race of a Norwegian species, whereas 

 the greater number rank it as an undoubted species 

 peculiar to Great Britain. A wide distance between 

 the homes ef two doubtful forms leads many naturalists 

 to rank both as distinct species ; but what distance, it has 

 been well asked, will suffice? if that between America 

 and Europe is ample, will that between the Continent 

 and the Azores, or Madeira, or the Canaries, or Ireland, 

 be sufficient ? It must be admitted that many forms, 



