1850.] Remarks on the variation of affined species, 223 



In several such cases where the sexes differ, the adult males only of 

 two or more races can be distinguished, as exemplified by Thamnobia 

 cambaiensis of N. and Middle India and Th.fulicata of S. India and 

 Ceylon, — also by some of the Indian long-tailed Nectarinice y — by 

 Tephrodornis pelvica and T. sylvicola, — by certain of the Kallij 

 Pheasants (Gallophasis) , and of the Tree Partridges (Arboricola) . 

 Or only the older males may assume a distinguishing mark, as in 

 Lanius superciliosus of the Malay countries as compared with its 

 representative in India. Or perhaps the old of both sexes may alone 

 be distinguishable, as instanced by the amethystine Chrysococcyx 

 xanthorhynchos of the Malay countries and its emerald-green Indian 

 representative. Lastly, the nuptial plumage may alone present a 

 constant diversity, which is very great in Motacilla alboides and M. 

 dukhunensis ; and we should infer that Hydrochelidon leucopareia so 

 common in India, and H. Jluviatilis, Gould, of Australia, were not to 

 be known apart in their non-breeding livery. 



That we should not be too hasty in setting down these slight and 

 apparently trivial differences as denoting varieties only of the same 

 particular species, is indicated by the fact that with a constant varia- 

 tion of colour, however seemingly unimportant, is sometimes, if not 

 commonly, associated a marked difference in the voice. This is very 

 decided in the case of Pratincola indica, nobis, as compared with that 

 of the European Pr, rubicola ; the wild Turtur risorins, (L.) of 

 India has also a very different voice (or coo) from the domesticated 

 Dove so common in cages and called by the same name : and we should 

 expect that the three Cuckoos before referred to will prove to differ 

 remarkably in voice ; while (so far as we can learn) the Bendronanthus 

 agilis of India never emits the fine musical notes of the very closely 

 affined D. trivialis. How excellent a criterion is furnished, in some 

 cases at least, by the voice is illustrated by the multifarious breeds 

 of the common domestic fowl, all of which speak the same language, 

 which is a very different one, in every note uttered, from that either of 

 the wild Gallus Sonneratii of S. India, or G. Stanleyi of Ceylon. 

 But a more conclusive proof, that exceedingly close external resem- 

 blance may subsist when the species are unquestionably diverse, is 

 deduceable from the fact of the very extraordinary conformation of 



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