Notices of New Books. 



8627 



of the existence of every conceivable variety of plumage between the 

 two extremes : the two birds have the same figure, the same habits, 

 the same voice, and build similar nests; and let them vary as they 

 may in colour, I can found no hypothesis on this variation farther 

 than this, that I believe them to constitute but one species, which in 

 colour is most inconstant. 



This variability is an old acquaintance with a new face : let the 

 entomologist study his series of Chelonia caia, Abraxas grossulariata 

 or Peronea cristana : let him take extremes of each ; and let him try 

 to persuade some expert in the science that these extremes are new 

 species. He will certainly be unsuccessful, simply because the ex- 

 pert would know better. May I venture to suggest that somewhat of 

 the same practical knowledge would assist the ornithologist, and 

 would preserve us from many of the long discussions we are now 

 compelled to read on the non-permanence of species. Well do I 

 recollect the time when we had dozens of these sub-species in Agrotis, 

 in Sarrothripus, in Peronea, but increasing knowledge is sweeping 

 them away : year after year they disappear from our catalogue, and 

 not an advocate is ever found for their restoration. But the geo- 

 graphical sub-species or species of birds are not around our doors ; 

 we see them dimly through a vista of books and skins ; and 

 " Distance lends enchantment to the view." 



" Some naturalists believe that permanent varieties are common in 

 the animal kingdom, and Kaup calls them sub-species. Such persons 

 consider that their differences from other individuals of what they 

 would term the typical form, do not entitle them to the full rank of a 

 species. Others, again, deny that permanent varieties exist, and state 

 their conviction that even slight differences of colour and size, if 

 found to be constant, are sufficient to constitute such individuals a 

 distinct race or species. When such differences are found to co-exist 

 with a different geographical distribution, T certainly prefer the views 

 of those who look on all permanent distinctions of colour, size, struc- 

 ture, &c, as distinct species ; and I believe that no change of climate 

 or food, or other external circumstances, will produce any alteration . 

 in them or in their descendants, if they remain true to each other; and 

 as yet I know of no recorded instance where any well-marked race 

 has produced offspring differing from their own, or tending to 

 revert to a supposed original type. That various nearly-affined spe- 

 cies will propagate, inter se, and produce fertile offspring, 1 fully 

 believe ; as in the cases of the green pigeons of Bengal and of 



